Update Mautic 5.2.6 -> 6.0.2 (composer-based)

Your software
My Mautic version is: 5.2.6
My PHP version is: 8.3.22
My Database type and version is: MariaDB 10.11.11

Your problem
I just moved a system running M5.2.6 over to composer (was non-composer install), following How to switch to Composer — Mautic Documentation 0.1 documentation, without warnings or errors during that step. The site has been running without visible problems.

I am now trying to upgrade (composer-based) to 6.0.2 following this guide: How to update Mautic — Mautic Documentation 0.1 documentation. I changed all occurrences of 5.2.6 to 6.0.2 in composer.json and ran composer update --with-dependencies.
This produces a lot of errors, and the php commands (cache:clear etc) don’t work anymore.

First, there are some warnings in this build step:

> npm ci --prefer-offline --no-audit
npm WARN deprecated osenv@0.1.5: This package is no longer supported.
npm WARN deprecated inflight@1.0.6: This module is not supported, and leaks memory. Do not use it. Check out lru-cache if you want a good and tested way to coalesce async requests by a key value, which is much more comprehensive and powerful.
npm WARN deprecated @npmcli/move-file@1.1.2: This functionality has been moved to @npmcli/fs
npm WARN deprecated rimraf@2.7.1: Rimraf versions prior to v4 are no longer supported
npm WARN deprecated rimraf@3.0.2: Rimraf versions prior to v4 are no longer supported
npm WARN deprecated glob@7.1.3: Glob versions prior to v9 are no longer supported
npm WARN deprecated glob@7.2.3: Glob versions prior to v9 are no longer supported
npm WARN deprecated glob@7.1.7: Glob versions prior to v9 are no longer supported
npm WARN deprecated glob@7.1.7: Glob versions prior to v9 are no longer supported
npm WARN deprecated debug@3.2.6: Debug versions >=3.2.0 <3.2.7 || >=4 <4.3.1 have a low-severity ReDos regression when used in a Node.js environment. It is recommended you upgrade to 3.2.7 o

Then, after updating themes and co. these errors. (Project root is /var/www/begegnung):

 [WARNING] Some commands could not be registered:


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In getSession_Storage_Factory_ServiceService.php line 24:

  Class "Symfony\Bundle\FrameworkBundle\Session\ServiceSessionFactory" not found


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").




 [WARNING] Some commands could not be registered:


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In getSession_Storage_Factory_ServiceService.php line 24:

  Class "Symfony\Bundle\FrameworkBundle\Session\ServiceSessionFactory" not found


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FieldModel.php line 478:

  Mautic\LeadBundle\Model\FieldModel::__construct(): Argument #6 ($fieldList) must be of type Mautic\LeadBundle\Field\FieldList, Mautic\LeadBundle\Field\FieldsWithUniqueIdentifier given,
  called in /var/www/begegnung/var/cache/prod/ContainerAtVkLkd/AppKernelProdContainer.php on line 4473


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").


In FilesystemLoader.php line 99:

  The "/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/views" directory does not exist ("/var/www/begegnung/vendor/friendsofsymfony/oauth-server-bundle/Resources/
  views").

Another observation (perhaps related??): Restoring the codebase (via restoring composer.lock and composer.json) and composer install does not work for me, but resets the site to the “Mautic is ready to install”. If it’s not related, I do not care about this.

Any help on these errors is greatly appreciated!