Sometimes a phone will warm up more if an app in the phone is using lot's of resource so the phone has to work harder to keep up or the phone is set to fast charge.
If Network Signal drops them the phone needs to work harder to maintain connection.
Perhaps try Safe Mode.
Put the phone in Safe Mode which disables your downloaded app's but let's your stock app's keep working. If the issues stop then this highlights a downloaded app as the possible issue. Come out of Safe Mode and start deleting your most recent downloaded app's one at a time until it stops. https://www.samsung.com/uk/support/mobile-devices/how-to-start-my-galaxy-device-in-safe-mode/
In regards to charging make sure the charging port is clear of debris via using a torch.
Can you try another Samsung charging brick and cord or charging pad / stand.
A phone picks up lots of junk files along the way which can affect the phone too.
Clear the phone's System Cache Files is a good generic troubleshooting tip.
Clear your phone's System Cache Files by turning your phone Off and then from a set series of button presses go into the phone's System Files and clear the cache. No information is lost this way. You may need to insert your headphones or hook upto a computer with your data cable to get to this menu on the phone. https://www.samsung.com/uk/support/mobile-devices/how-do-i-clear-the-cache-on-my-device/
A Samsung Experience Store or Samsung Service Centre can certainly take a look too.
Over time when a phone has been charged up and battery discharged the output of the battery will naturally discharge.
Current Phone >Samsung Z Fold³ 5G.
Previous Phone > Note 20 Ultra 5G SM-N9860.