So , I've had my s21 5g for about a week , noticed, when I'm using a video call or zoom , the phone gets very hot , I can see from reading the comments already I'm not alone.
Go to: Settings - Battery and Device Care - Battery - More Battery Settings - Processing Speed...
and check that the setting 'Optimised', is selected?
I noticed my phone gets hot when using the camera for extended periods of time, but i guess that's just due to the power it takes to operate it; I have my setting on 'High'.