So your device is visible in Studio Setup → MIDI Port Setup, is Active, and you’ve checked In ‘All MIDI Inputs’? If you click to Monitor through there, does it register any input?
TBH, C15 is a new installation on your Mac. So it needs new permissions for hardware access. It has nothing to do with C14.
I’m not sure if this will solve your problem, just saying it would be the first place I would search… So many reports in the past about Mac specific security settings affecting new installations.
Have you tried to turn off the midi controller while cubase is running, and then turn it on again without closing Cubase. Plug and play connection may have been interrupted.
Did you check the permissions on macOS settings, like st10ss suggested?
I don’t use Macs, but apparently should be somewhere in System Settings → Privacy & Security. I guess check for any permissions your standalone synths and Cubase 14 have, but Cubase 15 doesn’t, then add the same permissions for Cubase 15.
Have you only problem with midi output? Do audiotracks make sounds? If no sound from any tracks, check ‘Studio/audio connections/output’ , is the output configured or not?
I’ve been working with Cubase (Windows) for over 15 years and I have the exact same problem. In my opinion, version 15 is the worst update ever. I have to restart the program up to three times before it suddenly works.
I’m sure you don’t think it’s as simple as “MIDI doesn’t work in Cubase 15 and it has nothing to do with the configuration of my system.”
Please post some screenshots that show the relevant parts of your MIDI configuration–like MIDI Ports Setup in Cubase, and MIDI Studio in MacOS Audio MIDI Setup.
In Privacy & Security, does Cubase 15 have permission to use the microphone?
Do the VST instruments make sound when you use the in-plugin keyboard? The on-screen keyboard? If you don’t get sound even without using your MIDI controller, the issue is related to your Cubase 15 settings.
Do you use Control Room?
What audio interface are you using? It is selected? Post a screenshot of your Audio Connections - Outputs
On a MIDI track that’s assigned to use some VST instrument, do you have Monitor or Record enabled?
What exactly did you check? You’re leaving out all the details.