I think I remember some weird power bugs in the 2700x, though I never encountered them myself. The best thing I could find was this reddit thread https://www.reddit.com/r/Amd/comments/apw8im/ryzen_freezes_in_linux_even_if_linux_is_in_vm/

Do you still have the live iso you used to install arch? Does it work? Do other distros work (just the live systems are enough)?

Edit:

Some more things: Did you try disconnecting the pc from mains, pressing the power button (to discharge all capacitors) and reconnecting. Reseat the button cell for the bios?