Used to be able to change them manually in 5.2 with the following paths:
• Side menu logo: /mautic/app/bundles/CoreBundle/Resources/views/Default/navbar.html.twig
• Login screen logo: /mautic/app/bundles/UserBundle/Resources/views/Security/base.html.twig
From https://forum.mautic.org/t/customizing-the-left-side-menu-logo-in-mautic-5/35391
In 6 these are no longer valid I believe. Anyone have an update on this?