Just put the new PC together, booted up and nothing...red light for CPU on the motherboard. I've built countless computers but never seen this issue with new out of the box components. Is that a pretty much guaranteed bad CPU, or could it be a motherboard problem? I'd appreciate insight on next steps, since this is all new hardware architecture I don't have spare motherboards/cpu's to swap, my other pc's are zen3.
Can't you go to the shop and test it out there? Some motherboard take 5-10 minutes to get a FIRST post. Maybe this is the case? probably not because you have red light for cpu.
If you motherboard has a BIOS flashback function or the ability to flash the bios without a CPU, it might be worth trying to flash to a newer version of the bios if one exists.
When i built my firs X570 system i remember having to clear the CMOS before i could get it to post.