I am currently running Big Sur on a MBP 16" with a SpaceMouse Pro Wireless and the beta drivers you mentioned.
Am not a pro spacemouse user yet - but basic things seem to work fine.
I am not using it too heavily though as the need for a USB-receiver annoys me honestly haha - why can’t they make at least a USB-C version of their unifying receiver???
And I am also really missing the orbiting feature:
Furthermore button mapping does not really make sense to me, but that I guess is not a 3Dconnexion issue, but more sth that has to be fixed from the McNeel side…
Hope this is helpful, let me know if you have specific questions!
May I ask what Mac you are using right now?
Cheers