Big Sur 11.1 works. So does Catalina. I am running Big Sur on a 2017 MBP15" i7 and Catalina on a late 2012 iMac 27" i7. This works very well. However, my Catalina based 2020 MBP 13" i5 does not work with the iMac. Firewalls and permissions are pretty much identical. Any ideas?