Same! My watch had stopped working as my phone keep popping up saying plug in had stopped working and I have tried everything but nothing so far, I hope someone do know the solution, any advice would be appreciated!
I had slightly different problem after recent phone update with phone not updating activity recorded by the watch though the phone (s21) could still see the watch. Updating the wearable app fixed my issue. I also turned the watch off and back on again.
Did you try updating the wearables app on your phone? Mine appeared not to be updating automatically and seemingly need to be updated after doing the recent S21 update.