Hi and welcome!
I’m starting to believe there is an issue with recording on the JACK backend (without PipeWire) due to MIDI Controller input no workie
Most people I know (including me) use PipeWire and don’t have issues. So this needs further investigation from me. I will be tracking this issue here: Cannot record on pure JACK backend (MIDI or audio) (#4961) · Issues · Zrythm / zrythm · GitLab