In case someone runs in some weird errors on FDCAN, this confirmed works. You must initialize the complete txHeader structure otherwise you might get weird stuff on the bus. For example inconsistent IDs, remote frames instead of standard frames etc.
I was trying to do the same (transfer from Windows PC) to the H7 CPU, however the general problem with receive to idle seems to be, that the idle is triggered too fast, resulting in reception of 1 or just several bytes. For the embedded senders the i...