On an UEFI system with LUKS2/argon2 encrypted root (/), LUKS1/PBKDF encrypted boot (/boot) (and/via GRUB early crypto),
if desktop-base is installed (providing GRUB [emerald] theme), mkconfig/05_debian_theme will cause GRUB to prompt to
unlock the LUKS2 device to load the theme background, which silently fails (cryptomount: error: Invalid passphrase).

This causes GRUB to unnecessarily/annoyingly prompt twice for crypto passphrases, though it seems a quick work-around at
the LUKS2/root partition prompt is to simply enter an empty phrase to jump to the menu.

I understand LUKS2 GRUB support is a WIP; I do not know if this includes argon2 support.  It would be great to avoid
this annoying prompt situation (e.g. by detecting LUKS2/argon2 on the partition, or supporting the situation somehow;
preferrably still with a a single prompt in a manner similar to cryptsetup-initramfs/KEYFILE_PATTERN and
crypttab/keyfile spec).

Thanks!