Exynos heats more than a room heater, it's a well known fact, it'll get worse in the summer. Anyways you can take some measures to keep the heat down a bit. 1. Don't use the phone while charging 2. Do not use performance or maximum mode 3. Make sure not many apps are running in the background 4. Try to keep the brightness low, I know you need more brightness outdoors but I don't think max auto brightness is necessary because I also have the S21FE and tested it. 5. If you're gaming on the phone, stop it Exynos isn't for gaming. I hope these steps will help you a bit.
It will initially heat for some days after software updates because new update needs to get set with the OS. It's same for my s21 ultra. After some days it becomes normal.
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