Apple M2 Pro

If your motherboard does not already have a heatsink, add a third-party one like the Arctic M2 Pro, Thermalright TR-M.2 2280 Type A, or Be Quiet MC1.

I'd just sell the known good components for as much as I could and put that towards the Mac Mini M2 Pro. I feel like that would be a much, much better investment than the upgrades you're considering.

Get the Patriot P400 Lite or Crucial P510; if your unknown motherboard does not have an M.2 heatsink, add a third-party one like the Arctic M2 Pro, Thermalright TR-M.2 2280 Type A, or be quiet MC1.

A "high-end gaming PC" should have a motherboard with an M.2 heatsink. If not, you can a third-party one like the Arctic M2 Pro, Thermalright TR-M.2 2280 Type A, or be quiet MC1.

Any PS5-compatible heatsink should fit. Consider the Arctic M2 Pro or Thermalright TR-M.2 2280 Type A.

I have! Also considering a Mac Mini M2 Pro at a very good price. But since I already have. a nice build and case, I was also considering upgrading the mentioned parts, which would cost me less than a Mac.

The thing is, you don't even need to go for M4 (or M5), even M2 and M3 Pro/Max units are fast as heck, even faster because more cores.