I9 9900K cores high temperature on Fedora 31

Hmm. Scythe is a good manufacturer. I don’t have an i9 personally, I’m getting up to high 60s/low 70s at sustained 100% load with air cooling on a 8c/16t ryzen with the same TDP, but it could be that 9900K truly does run so hot that it needs liquid cooling, that sort of talk is the reason I passed up the i9 tbf

You could try x264 or Prime95 benchmark and see how your numbers and temps compare to other people on the internet. If you have any doubts about thermal paste, better repaste the CPU and reseat the heatsink, that would be the cheapest way out. You could also underclock if this stability problem is important enough for you