Sadly, the issue with inability to boot right after enabling XMP profile for Corsair DDR5 is not my impatience as of BIOS v20. After upgrading to v21, same thing: boots fine with XMP disabled, but as soon as it's enabled, infinite loop of codes including 54 and 5C. Very interestingly, a forced power down and restart escapes the loop and the machine boots normally. The last BIOS version that did not do this was v20b, which was since removed from the list of available BIOS versions for this motherboard.