set prefix=(hd0,1)/boot/grub
set root=(hd0,2)

insmod linux
insmod normal
normal

set pager=1

ls
 -> (hd0,gpt1) (hd0,gpt2) ...

ls (hd0,gpt1)/

set root=(hd0,gpt1)

linux /boot/vmlinuz root=/dev/sda1
initrd /boot/initrd.img

boot

vi /etc/default/grub 
...
GRUB_DISABLE_OS_PROBER=false

vi /etc/grub.d/30_os-prober
...
      for LINUX in ${LINUXPROBED} ; do
        LROOT="`echo ${LINUX} | cut -d ':' -f 1`"
        LBOOT="`echo ${LINUX} | cut -d ':' -f 2`"
        LLABEL="`echo ${LINUX} | cut -d ':' -f 3 | tr '^' ' '`"
        LKERNEL="`echo ${LINUX} | cut -d ':' -f 4`"
        LINITRD="`echo ${LINUX} | cut -d ':' -f 5 | tr '^' ' '`"
        LPARAMS="`echo ${LINUX} | cut -d ':' -f 6- | tr '^' ' '` consoleblank=180"
...

set default="0"
set timeout="5"

insmod gpt
insmod part_gpt
insmod fat
insmod chain

menuentry "GNU/Linux" {
    set root=(hd0,gpt2)
    linux /boot/vmlinuz-6.6.15-amd64 root=/dev/sda2 ro
    initrd /boot/initrd.img-6.6.15-amd64
}

menuentry "EFI Boot" {
    set root=(hd0,gpt1)
    chainloader /EFI/Boot/bootx64.efi
}