https://wccftech.com/galaxy-s21-series-finally-getting-stable-android-12-based-one-ui-4-0-update/

The time is finally here. Samsung has announced that it is rolling out the stable Android 12-based One UI 4.0 update to the Galaxy S21 trio of devices. The news is coming after a two-month-long One UI 4.0 beta program for the One UI devices. Most of the changes that Samsung is introducing in this update have been available in the beta program ever since it started.

However, you are now getting the definitive experience, and the update rolling out today will be much more polished and bug-free than the previous updates.