I’ve been having the same issue for a few months with my Beelink SER5 5500U; random restarts even though the temperature is fine and memory tests show no errors.
This week I even decided to completely reinstall the system, but the problem still persists.
@EEdithson, did the BIOS update finally solve the issue for you?
I’m also attaching a photo of my PC in case it helps to check if a BIOS update is available for my model.

Thanks in advance!