HWMonitor for detailed information on temperatures (CPU, individual cores, VRM, chipset and GPU, even SSDs) or even basic RyzenMaster for quick CPU temp.
The frequencies are ok, that's how turbo boost works. It's affected mainly by load (secondary by threads amount utilized).
It can be GPU driver as well if you are using Optix denoiser. The latest Ampere drivers are pretty fresh out of the box, with plenty of issues reported. Try Studio driver, it's more conservative.
Under normal conditions, 3990X should go up to 70C with U14S in well ventilated case and average room ambient (25).
It wouldn't crash if it was hot though. It would just downclock further, but like..a lot further.
Lastly, most common culprit, esp. if it crashes the whole Windows, not just software, could be memory due to unstable profile. Not sure what the particular XMP/DOCP settings are for your Vengeance kit.