This is a special devExtreme / devExpress bundle for symfony 5+
Just place the src/AppBundle folder into src. Bind it under services.yaml. Thats it. Symfony will detect it as user's own AppBundle and load it by default.
add in services.yaml
add key
App\AppBundle:
and line below it.
resource: "../src/AppBundle/"
https://isgoodstuff.com/2021/04/11/devexpress-grid-to-symfony-controller-doctrine-part-1/
https://isgoodstuff.com/2021/04/11/devexpress-grid-to-symfony-controller-doctrine-part-2/