Looks like GRUB has issues loading EFI binaries from (cd0), which is what would be used in e.g. qemu with OVMF with `-cdrom`. Apparently also what is used with AArch64 + U-Boot USB.
*** NixOS *** NixOS is a Linux distribution based on the purely functional package management system Nix. More information can be found at https://nixos.org/nixos and in the manual in doc/manual.