Plenty of posts on here about A12 OneUI4 - some positive, some negative. Appears it has been buggy for a fair few people, but personally I've not had any significant issues. A second update for some devices which included the Feb security patches rolled out last week. Would advise clearing the system cache after you've updated just to clear any rouge leftovers from past firmware, along with running Galaxy App booster.
When you update the phone the battery will show you Zero Percentage on it I have update mine already and that the only thing I had everything Else is fine so just be ready for what happens I just hope it doesn't happen to you take care my friend