According to the gpart() man page:-
How big does it need to be and what goes on it?
I'm intending to use GRUB as a boot manager, so should I install a bios-boot partition as the first partition on a GPT disk?bios-boot The system partition dedicated to second stage of
the boot loader program. Usually it is used by
the GRUB 2 loader for GPT partitioning schemes.
The scheme-specific type is
"!21686148-6449-6E6F-744E-656564454649".
How big does it need to be and what goes on it?