I never update immediately as this is a work machine, but I wondered if it's just a straightforward affair or is there anything to be aware of (say set SecureBootModel to something other than Default or disabling fTPM before hitting upgrade?
As long as you've got everything up to date it should be straightforward.
Just tried the SmallTree from the resources part of this site, but no luck - shows no media connected. Apple2xx continues to work, but is offline after sleep. So all as before...Anyone know if Smalltree is working in 12.1?