Hey Fabian! Welcome to the community :))
It’s technically possible I think, but complicated using this technique:
And having two “contain” Filter grouped with “or”. This is complex, but if you really need it feel free to reach out.
A less complicated route is using lookups. You can add a lookup field on the TestModuleType database to pull the TestProjects using the TestModule field.
If you need it as a relation field, you can have an automation run triggered when the lookup changes, populate the same values in the relation field.
Not sure if this is exactly what you need, but you can play around some more from here :))