If I am right you use the phone mostly for video and Camera.
Here are my theories.
The charger you use might have had an effect especially if its a faster charger the S21 can't handle ( s21 need slower charger)
Maybe Samsung still hasn't optimised the phone for long usage of camera and video and it somehow messed it up.
Somebody in the house dropped or mishandled your baby
👶 without your knowledge.
😝 Just theories don't take them seriously, Especially the last one but something to think about while you wait.
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