Mines can get warm but typically I've not had much overheating issues. To touch anyway. I have however noticed that it's really laggy opening and closing tabs. Sometime finger presses take seconds to respond. The adaptive frame rate seems to be making it quite stutters too. I know it is down to 8GB for my basic 128GB version but compared to my s21 Ultra this is insane.
So not long after I posted my message above I was co templating returning my device. I checked it had no updates to do which it never. It got to the stage where I could count in seconds the fingerprint to unlock. I had ran Geekbench a few times over last few days. Scores should range between 1100 and I was getting this range. Even as low as 600. Highest 900.
I decided to simply restart the phone to see if that helped. As soon as I unlocked it after this I noticed a huge improvement. No lag and back to the snappy flicking between apps. So before losing all hope folks just try a simple restart. Geekbench score after this was 1100!