This type of problem is hard to diagnose over the internet. If it landed on my bench I would remove and install the logic board into a known good housing this would rule out or confirm if it’s a parts issue or a board issue but unfortunately this is not feasible for most people.
When it comes to temperature warnings the first thing I would be looking for is NTC lines "Negative Temperature Coefficient" The NTC circuits I would rule out first are:
· Lattice Projector.
· Power button.
There are other NTC circuits that can also become faulty due to cracked or torn pads between the two layers of the board. However I would defiantly try replacing the power button flex assembly first as this would be the most likely culprit. You could also try and boot with the lattice projector disconnected but I cannot remember if this will cause it to restart.