The grub2 loopmount stanza I use does not use the /boot/grub/loopback.cfg which is a file inside the ISO. Probably a better way.
I sometimes have had to open ISO to find boot parameters to get grub boot stanza parameters or details to get it to work.
I have used grub2 to boot Debian & Fedora.
For newer users I find the set up of Ventoy to be easier and it boots just about anything. I still use grub2, but created a Ventoy flash drive which also boots Windows.