The answer is exactly what you think. The training story is BS (at least in part). Many of the cars unofficially support Sophy.
F3500 B is the same car as the F3500 A, so why is it that Sophy doesn't officially support the B? You can use the glitch and the F3500B works great. There's likely some type of config file that each car has, and sure some of them could be copied to other cars. For all the new cars (post launch) there is no excuse. They should all support Sophy. Same with all tracks.
This is where I believe the PS4 support is hurting the PS5 version. Four years ago, cross platform support was cool. Now, not so much.