Mautic can not run, after install mautic with Composer

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Your software
My Mautic version is: core mautic 4.0
My PHP version is: 7.4.3
My Database type and version is: MariaDB 10.5.18

Your problem
My problem is: install with composer , and error message when open mautic webpage: mautic.mydomain.com

These errors are showing in the log:
error message on page: Composer detected issues in your platform: Your Composer dependencies require a PHP version “>= 8.0.0”
Steps I have tried to fix the problem:

  1. reinstall the mautic with composer, same issue.
  2. resinstall ubunt 18.04, reinstall mautic with composer, same issue.
  3. resinstall ubunt 18.04, reinstall mautic with composer, run composer update, same issue.
  4. Edit composer.json, do “platform-check”: false, reboot the server, same issue.
  5. resinstall ubunt 18.04, reinstall mautic with composer, install php8.0, same issue.

The article referenced is :

thanks for all patience.