So... I figured it out, and it's the worst kind of stupidity on my part.
Started having trouble with reboots not moving past BIOS again. Figured it had to be mechanical, because BIOS was flashed to latest update. CMOS cleared, new CMOS battery. New USB drive w/fresh boot files from Unraid, etc., etc., I even went through and removed all SATA cables and the NVMe thinking I could reconnect one by one and replace as needed. No change despite nothing connected.
Then I realized, I still had a wired keyboard attached sitting behind the computer. Legacy vm hardware.
Turns out, the sea of wires back there was squashing the delete key on that keyboard, which is one of Asrock's BIOS entry keys. So stupid. Pulled the keyboard out from back there.. system booted right up past BIOS.
I should've known because it would never give me the boot menu even when I was smashing F11 (Asrock's boot menu key). I knew it had to do with THAT part, but couldn't figure it out and was pulling my hair out. It always ignored my F11 input and went straight to the BIOS.
SOLVED = my stupidity (smh).