Hey there. I withdrew my phone from Beta One Ui by > Samsung Members app > messges > One Ui 5 Beta notice > One Ui Beta status > click withdraw >( ensure you have a back up of EVERTHING via Smart switch and copy every bit of data onto Google Drive etc >restart your device.> connect your device to a Pc running the very latest Smart Switch > run revert /install previous software. THIS WILL WIPE YOUR DEVICE SO BE SURE YOU WANT TO DO THIS AND ENSURE YOUVE BACKED UP EVERTHING INCLUDING CONTACTS ETC BEFORE YOU COMMIT >Smart Switch will then download and then upload Andriod 12 and One Ui 4.0 to your handset.
Why do you want to downgrade , is there something myself and other experienced and experts can help you with ? Please don't hesitate in contacting me again ill be happy to assist you.... Good luck with which ever way you choose to go .
All the best 👍