Samsung Galaxy Note20 gets hot or shows a temperature warning

The checks in more detail

take off the case, charge without heavy use, set the refresh rate to 60 Hz, lower the camera's video resolution, and check Settings, Battery and device care, Battery for an app with high background use. The S Pen and its sensors do not cause heat. Heat while charging is common with fast charging at 25 W; turn off Fast charging as a test. A weak signal makes the modem work harder, so use Wi-Fi at home. Wipe the cache partition after the final update, restart, and test in Safe mode.

A phone that overheats with nothing running, shuts down or has a swollen back has a failing battery and needs service. Samsung Members' battery and temperature diagnostics help. Samsung Members has a Temperature check in its diagnostics that shows the battery's temperature and warns when it is too high. The Note20's S Pen charges inside the phone and draws a little power, but it is not a heat source. If the phone is hot only while using the camera at 8K, the video mode is the cause, and 4K is a cooler default.

If the phone gets hot while charging wirelessly, the wireless charger is adding heat; the Note20 supports it, but a phone in a case on a pad is warm by nature, and the cure is a cooler pad, no case and no heavy use. Fast wireless charging can be turned off in Charging settings for a test. A phone that is hot after a game should be allowed to rest for half an hour.