The Connection to other DCC apps is important to us.
Sorry for the delay; I had a week off and checked only the Q&A and Help Forum. Admins typically ignore Q&A questions posted here, as those questions are misplaced.
This is the site issue forum, and I can't find an entry you have problems signing in.
Since you recently bought Cinema 4D, enabling access should be no problem. Please open a new post with your access problem.
My tip: can you reimport the FBX to Maya to see what it has produced? Since Autodesk bought FilmBox ages ago, they have a proper working roundtrip. Hopefully, the result will allow us to solve this in case something has changed.
Some people have good results with the DAE_FBX format, which (AFAIK) has a triangulated check box.
Have you tried to use the Mesh> Cut> Untriangulate?
The round trip in Cinema 4D 2024 works fine; no new triangles exist. Yes, I test constantly, as answering from memory is typically not up-to-date; things can change quickly.
Or check with Support:
All the best