can you switch your system to UEFI boot? That fixed it for me.
Change the BIOS to UEFI. and possibly(!) reinstall via UEFI boot so it makes the EFI partition(s).
Set primary console to EFI, no secondary console? System: Settings: Administration.
Section "Console", vt driver should be enabled, primary to "EFI Console", secondard to "None"
What OPNsense installer image are you using? VGA or Serial?