I read the post today and since I myself have these overheating problems with the battery on the S21 +, I tried a few things.
Make sure there are no apps running in the background that can reduce battery consumption. You can deactivate the background use of individual apps in the app settings.
The low frame rate must be activated in the Game Booster settings.
Choose the graphics setting you want, maybe Balance first and see how the battery temperature evolves.
After that, I was able to play non-stop with these settings without my smartphone reporting any problems.
Hope that helps a bit.