Set it to constant 4.35GHz@1.181V in BIOS manually, disable all boost-related features and hyperthreading. Test for temperatures.
If it's still 90°C - then daym, son, check your cool. Maybe get an air cooler just to be sure.
If it got cooler - then your mobo auto boost features are junk. Use manual overclock.
I run a 5800X myself and it's set to 4.35@1.181 which is more than enough for anything, unless you want to impress the Internets with your benchmarking. Alternatively, use Clocktuner for Ryzen (CTR) 2.0 for per-core configuration - it supports 5000 series since last week. I'd use it myself but what I have is already enough and in excess. Maybe in half a decade when it starts bottlenecking.