sysctl machdep.bootmethod
You may need to mess around with efibootmgr(8) to add a UEFI boot entry. But you need to be UEFI booted to use it. As the install media apparently correctly booted with UEFI you could use that, just pick the shell option.It seems UEFI boot is not available. Installed with Auto (ZFS) and GPT (BIOS+UEFI). Is it necessary to run manual command to fix/init uefi boot?
Some older boards have a 32 bit UEFI, that won't work. But then the OP wouldn't be able to UEFI boot the install media either.I can remember that some older mainboards do support UEFI but can only work with normal entries.