At the moment, it is not possible to install _both_ grub-efi-amd64 and grub-pc, and keep both maintained correctly.
We can install both grub-pc-bin & grub-efi-amd64-bin (& grub-efi-amd64-signed) but only one of them will be updated.
So imho, for now, if we booted in bios mode we should install grub-pc + grub-efi-amd64-bin, run grub-install --target x86_64-efi, and then install grub-efi-amd64-signed.
So this depends on our goal.
At the moment, it is not possible to install _both_ grub-efi-amd64 and grub-pc, and keep both maintained correctly.
We can install both grub-pc-bin & grub-efi-amd64-bin (& grub-efi- amd64-signed) but only one of them will be updated.
So imho, for now, if we booted in bios mode we should install grub-pc + grub-efi-amd64-bin, run grub-install --target x86_64-efi, and then install grub-efi- amd64-signed.