https://github.com/a1ive/grub2-filemanager/releases
git clone https://github.com/a1ive/grub2-filemanager.git
cd grub2-filemanager
./update_grub2.sh
./build.sh
DO NOT boot grubfm.iso with memdisk!
map --mem /grubfm.iso (0xff)
map --hook
chainloader (0xff)
linux /loadfm
initrd /grubfm.iso
chainloader /grubfmx64.efi
loader /grubfmx64.efi
efi /grubfmx64.efi