I just finished a new article that could be considered a follow up to my previous BridgeOS update & restore article. I talk about how BridgeOS updates work and how you can now downgrade from a beta version of BridgeOS (Big Sur) to a native production version (Catalina). This was previously impossible. In the past you had to wait until a more stable beta BridgeOS or wait until the next os went live.
My previous article on how to restore or update BridgeOS.
If you are having issues after you downgraded from Big Sur to Catalina on your T2 Mac, this might help you.