Unfortunately, I don't have Big Sur, and like all Apple upgrades, under no circumstances will I install it until I absolutely have no choice.
However if you care to post an issue here at
https://github.com/colin-campbell/firestudio-catalina/issues (yes you have to sign up for a free Github account), describing in detail your particular problem and your computer/interface configuration, I will try my best to help you troubleshoot. I can't for obvious reasons provide "support" for an unsupported configuration on the Presonus forums - so post to Github and I will look, Unfortunately no guarantees.