There seems to be problems loop mounting ISO files with grub 2.04, how to downgrade to grub 2.02? 

Grub 2.02 works for loop mounting ISO files on a Bootable pendrive.

I think the main problem comes when booting in UEFI mode. 

Reference: Grub command `loopback loop…` does not work on Ubuntu 19.10 [Grub command `loopback loop...` does not work on Ubuntu 19.10](https://askubuntu.com/questions/1186040/grub-command-loopback-loop-does-not-work-on-ubuntu-19-10/1186060#1186060)

Further Reference: LaunchPad <https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1851311>