After months of debugging, the random reboots of Ryzen 3700X/AMD GPU could be solved by changing the grub configuration to
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash amdgpu.ppfeaturemask=0xffffbffd"
which seems to help quite a number of people if 'journalctl | grep -i "hardware err"' returns errors like bea0000000000108 and microcode 8701021 or 8701013. From this thread:
https://bugzilla.kernel.org/show_bug.cgi?id=206903#c135
