I think that’s enough to return it to the shop you bought it from. That shouldn’t really happen at “stock” settings (in quotation because every motherboard manufacturer seems to know better than the chip maker, for some reason).
Have you tried using OCCT or AIDA64 to see if the same happens? It could be that the insane load Prime95 puts on the system make it crash, but it would otherwise work fine in every other application imaginable. What temperatures is reaching at full load?
But still, even after all these questions and tinkering I think that CPU is not working as it should.
I knew the same and some Youtubers that upcycle or fix PCs with older Ryzen 3000 CPUs report seeing many failed ones.