LUKS2 is only partially supported by GRUB; specifically, only the PBKDF2 key derivation function is implemented,
which is not the default KDF used with LUKS2, that being Argon2i (GRUB Bug 59409). LUKS encrypted partitions using
Argon2i (as well as the other KDF) can not be decrypted. For that reason, this guide only recommends LUKS1 be used.
Doesn’t GRUB support LUKS2 nowadays? I know that wasn’t the case a year ago or so, but I didn’t see a notice on the Archwiki last time I checked.
Not sure how up to date this is, but it claims LUKS2 is only partially supported by GRUB https://docs.voidlinux.org/installation/guides/fde.html