What motherboard? What cpu did you have? Is this new Ryzen 5600 on the hardware list for the motherboard? If so, are there any voltage, stepping or other settings (listed in the manual) required to make it run stably?
Make sure the new cpu is clean with no potential shorts from anything. Also ensure good heatsink contact. If you’ve done all the normal and necessary steps then yes it might be a bad cpu, but they aren’t frequent failure items in my experience. Disagreeable conditions for the cpu is more commonly the culprit. Engineering sample cpus are the most fickle, but even some normal batch cpus might sometimes require a bit more (or less) juice or a system tweak.
No, I would search for your motherboard model and forums to see what situations might match yours so that you might glean something useful as far as settings go. A quick check revealed nothing useful that stands out to me. Resetting all electrical connections was the lone useful tip. (The reddit link blocked me, lol. Fine) Perhaps more detailed (or different) search terms would produce better results.
I think you’ve taken the right steps to this point. Another CPU to test with would prove useful (though your original should suffice). Or another board to test this CPU in. Perhaps the shop you procured this one from has one or the other? Otherwise, I would pursue replacement.