Hello Jean Carr,
I found to withdraw from the beta program, you will need to do the following, which includes resetting your phone, but you can back it up first if you have the smart switch software installed.
From Samsung Members -> Settings -> One UI Beta Program Status -> Withdraw. Then plug the phone into your PC, and open up the PC version of smart Switch. Be sure to back up your phone since downgrading requires a factory reset. We recommend you try backing up your device and performing a master before moving back to Android 12.
Oddly enough, you cannot switch the beta to light mode reported here.