Grub2/ISOBoot of ubuntu 20.04 is failed in the grub 2.06 of ubuntu 22.04

Question

Ubuntu 20.04 iso installation using 40_custom, is failed in the grub 2.06 of ubuntu 22.04 LTS desktop.

I add the following code to below of 40_custom.

menuentry "Ubuntu 20.04.05 ISO" {
   isofile="/home/<username>/ubuntu-20.04.5-desktop-amd64.iso"
   loopback loop (hd0,gpt4)$isofile
   linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile noprompt noeject
   initrd (loop)/casper/initrd
}

(hd0,gpt4) is ubuntu 22.04 LTS. And grub version is 2.06.

The following error occurs.

error : out of memory.

kernel panic not syncing vfs unable to mount root fs on unknown block 0 0

the partition is constructed as follows.

Disk /dev/nvme0n1: 
Disk model: Samsung SSD                      
Units: 
Sector size (logical/physical): 
I/O size (minimum/optimal): 
Disklabel type: gpt
Disk identifier:
Device           Type
/dev/nvme0n1p1   EFI System
/dev/nvme0n1p2   Microsoft reserved
/dev/nvme0n1p3   Microsoft basic data
/dev/nvme0n1p4   Microsoft basic data
/dev/nvme0n1p5   Windows recovery environmet
/dev/nvme0n1p6   Linux file system

The window 10 was installed, then, ubuntu 22.04 is installed.

Solution :

When ubuntu 20.04 iso file is used, the rmmod tpm must be added as follows.

menuentry "Ubuntu 20.04.05 ISO" {
   rmmod tpm
   isofile="/home/<username>/ubuntu-20.04.5-desktop-amd64.iso"
   loopback loop (hd0,gpt4)$isofile
   linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile noprompt noeject
   initrd (loop)/casper/initrd
}