Samsung resumes rollout of stable One UI 4 based on Android 12 after fixing bugs
Samsung's stable updates to One UI 4 based on Android 12 for the Galaxy S21 family and the Galaxy Z Fold3 and Flip3 were halted last week due to a nasty issue with Google Play compatibility. Now, about five days later, the issues seem to have been sorted out through some collaboration with Google over the holidays, as the rollouts are finally restarted.
There's a new build doing the rounds, and this is labeled G99xBXXS3BULC for the S21 models (where "x" is a number that varies according to which device you have). The Korean variants get G99xNKSS3BULC. On the other hand, the new build for the Flip3 is F711xxxS2BUL6, while the Fold3 gets F926xxxS1BUL6 (here the "xxx" part varies according to region).
If you have one of these devices, you can manually check for an update and you might get lucky. As usual, carrier-specific models may lag behind unlocked ones.