Ok, I spoke too fast, the problem reappeared after several cycles but now I think I finally nailed it. The culprit seems to be hibernation mode. Even though I have it set to go to sleep when closing the lid and everything else, mine went into hibernation after being in sleep mode for several hours. By deactivating hibernation through the powershell, it now seems to be working perfectly!
My Inspiron 7620 (with RTX 3060) overheats when it is in sleep mode, with the GPU reaching 80 degrees C according to task manager after about an hour of being in sleep mode. When it is taken out of sleep mode the area around the keyboard and on the back feels hot and the fans quickly turn on and cool it back down. This happens regardless of whether the AC adapter is plugged in or not and both when the lid is shut and when it is open. The laptop is always placed on my desk when in sleep mode. The device does not overheat at all when it is in use, even under heavy load. It has been overheating like this since I got the laptop new about a week ago. I have checked the dell update app, the dell website, windows update and Nvidia geforce experience - the BIOS and all drivers are up to date. I ran a diagnostics test and all tests were passed successfully. Strangely, this problem does not occur if the device has been restarted prior to being put in sleep mode (as in actually clicking the restart button, not just shutting down and turning back on again), but the problem returns and it overheats again if put in sleep mode after it was previously shut down.
Inspiron 7620, overheats when in sleep mode