Is it possible to boot Ubuntu Core 20 on a bare metal AMD64 device from its own harddrive, and not a flash stick? I know it can boot from a flashstick, or in a VM, but can it boot on a real machine off its own harddrive?
yes there are 10000s of commercial devices out there doing that every day
if it does not work for you there might be some incompatibility with UEFI or a missing controller driver or some other bug involved.
there are plenty of commercial customers canonical has that have their devices flashed in the factory to the internal disk to boot from there by default …