Booting an ISO file from GRUB

[Marko Toivanen]

I have been trying to find information related to the following problem:

I'm trying to start a Lubuntu 22.04 installation from an older Lubuntu 
14.04 installation by booting the ISO file from grub menu.

Booting the ISO file works by adding the following menu configuration to 
file /etc/grub.d/40_custom:

menuentry "Linux ISO to RAM" {
    insmod lvm
    insmod ext2
    set root="lvm/lubuntu--vg-root"
    set isofile="/home/user/lubuntu-22.04.3-desktop-amd64.iso"
    loopback loop $isofile
    linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile 
toram
    initrd (loop)/casper/initrd
}

The problem is when Lubuntu 22.04 starts this way, there is a device 
"/dev/lubuntu-vg" showing up in Linux (what I didn't expect) and because 
of that, I can't make a clean install of Lubuntu 22.04 on the hard drive 
when Lubuntu was started from the ISO file (which is located on the hard 
drive).

My initial thought was that using "toram" option would completely load 
the ISO to RAM, so I could then be able to repartition the hard drive 
without having to start Lubuntu 22.04 installation from an USB stick.

When I try to repartition /dev/sda (where this lubuntu-vg is located) 
with gparted, I get the following error message:

"we have been unable to inform the kernel of the change, probably 
because if/they are in use"

So, is it possible to boot an ISO file so the problem described wouldn't 
happen?