Basically just the CPU fan, case, and PSU (if you're lucky). If someone can figure out how to get Doom running on just those 3 things, young people will be able to ascend.
They're also close to buyitforlife territory. Mine is >15 years old (1st gen i5!). The AM4 mount would've been free if I had the original receipt. But alas, I had to fork out $10 cause I was too dumb to have taken a photo of it back then.