Take a look at YouTube reviews for some current phone's and if you have friends or family or work colleagues with a phone your possibly interested in then ask to have a look.
Normally I would suggest to visit a Samsung Experience Store or Highstreet Store that has working retail demo models in to have a play but due to these unprecedented time's and lock downs they'll be probably closed.
Not all Samsung Galaxy s21 phone's are overheating so it's not clear why this is happening with some phone's and not others.
Some who use my model of phone reported overheating too but I've experienced none !
Enjoy the journey @kellyD
Current Phone ~
Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+
Samsung One Ui 3.1/ Android 11.