Hello !
I tried your custom.config to boot last manjaro-cinnamon-21.07.iso
no success.
Complaining about squashfs to ram and abort.
If i remove copytoram, abort also but later.
So i searched and find this (adapted for me):
menuentry “Boot iso Manjaro 21.07” {
set iso_path="/mnt/ISO/manjaro-cinnamon-21.0.7-210623-linux510.iso"
search --set=root --file $iso_path
probe -u $root --set=iso_disk
set iso_device="/dev/disk/by-uuid/$iso_disk"
loopback loop $iso_path
echo ‘Lancement en cours, patientez …’
probe -l (loop) --set=klabel
linux (loop)/boot/vmlinuz-x86_64 img_dev=$iso_device img_loop=$iso_path misobasedir=manjaro misolabel=$klabel copytoram driver=nonfree lang=fr_FR keytable=fr tz=Europe/Paris
initrd (loop)/boot/amd_ucode.img (loop)/boot/initramfs-x86_64.img
}
This one works for me.
What it the difference between yours and this one, i am not an expert…