This requires uploads of grub2 and grub2-{un,}signed to focal to bump the versioned number in the Replaces (grub2-common) and ensure upgrades from bionic to focal get a newer grub-efi-* with the correct lack of conffiles.
> How can you introduce conffiles in grub-efi-amd64 & grub-efi-arm64 which is shared across releases?
By not sharing it across releases.
> That will cause a mess in focal+ then, since it will conflict with grub2-common there.
Not with separate uploads to bionic and focal.
Which is less of a mess than having grub2-common in < focal having to declare a Replaces: on the versions of the grub binaries from grub2 source shipped in those releases.
This requires uploads of grub2 and grub2-{un,}signed to focal to bump the versioned number in the Replaces (grub2-common) and ensure upgrades from bionic to focal get a newer grub-efi-* with the correct lack of conffiles.
> How can you introduce conffiles in grub-efi-amd64 & grub-efi-arm64 which is shared across releases?
By not sharing it across releases.
> That will cause a mess in focal+ then, since it will conflict with grub2-common there.
Not with separate uploads to bionic and focal.
Which is less of a mess than having grub2-common in < focal having to declare a Replaces: on the versions of the grub binaries from grub2 source shipped in those releases.