Comment 5 for bug 1872463

I think I found the problem!

On x86_64
# Skeleton configuration file which finds the real boot disk.
cat >"$workdir/grub.cfg" <<EOF
if [ -z "\$prefix" -o ! -e "\$prefix" ]; then
 if ! search --file --set=root /.disk/info; then
  search --file --set=root /.disk/mini-info
 fi
 set prefix=(\$root)/boot/grub
fi
if [ -e \$prefix/$platform/grub.cfg ]; then
 source \$prefix/$platform/grub.cfg
elif [ -e \$prefix/grub.cfg ]; then
 source \$prefix/grub.cfg
else
 source \$cmdpath/grub.cfg
fi
EOF

is used inside the monolithic/gcdx64.efi

However, during d-i build, self-built bootaa64.efi is used with:
 cat >"$workdir/boot/grub/grub.cfg" <<EOF
search --file --set=root /.disk/info
set prefix=(\$root)/boot/grub
source \$prefix/$platform/grub.cfg
EOF

The monolithic one is the one that gets signed, and imho we should use that one on arm64 for now.