Figured
this article would be appropriate for this thread.
In theory, liquid metal used to cool CPUs is not a problem. The cooling mechanism and the CPU are so tightly pressed that nothing should spill or "fall" (when the right amount has been applied) because of gravity alone, and this is why there is generally no concern with using a motherboard vertically, even when you're using liquid metal.
However it appears that several cases have shown that the PS5's "seal" between the APU and its cooler can sometimes move or be damaged. When that is the case, if your PS5 sits horizontally, the liquid metal will stay flat and keep most of its thermal properties to help cool the PS5. But if your PS5 is vertical and "something" bad happens to the seal, then there is a risk the liquid metal will progressively fall down, becoming uneven, impacting its cooling ability and possibly reach components it shouldn't.