Rhinoceros 5 won't connect to Matrix 9 (I also have Matrix Gold)

Several things could be going on here.

This has recently been reported and solved by users with a similar setup … Matrix 9 Menu Bar Unresponsive

Secondly, note that Rhino 5 is not supported on Windows 11, although there are many who have been able to use it, but its safe to assume Matrix could also run into issues with the newer OS as well.