Update from macOS Big Sur public Beta to official release
The public beta FAQ covers how to de-enroll from beta builds.

https://beta.apple.com/sp/betaprogram/faq

See the Support section.

At any time, you may unenroll your device so that it no longer receives these updates. Then, when the next version of commercial software is released, you can install it from iOS Software Update, the Mac App Store, tvOS Software Update or watchOS Software Update.

https://beta.apple.com/sp/betaprogram/unenroll