Currently the contao/manager-plugin is only unlocked for up to Symfony 5. However there is a bug with symfony/web-profiler-bundle (see symfony/symfony#46650). While this fixed in version 6.1.2 of symfony/web-profiler-bundle the new version now requires version ^6.0 of symfony/http-kernel. Thus version 6.1.2 cannot be installed in Contao 5 as contao/manager-plugin still has a maximum dependency of ^5.0 on symfony/http-kernel.