How to downgrade grub from 2.04 to 2.02 on ubuntu 19.04?

Solution 1:

I started by suggesting:

One simple way to get grub 2.02 is to install an older version of Ubuntu for example 18.04.1 LTS alongside the other operating system(s). Then run sudo update-grub to get access to the other operating system(s). It costs a few GB, so there might be better methods.

You brought this idea one step further:

Ah Ha! So for an ISO booter, I use mkusb to make the foundation using say 18.04 and then it should have no problem booting 19.10 and newer ISOs. Very clever. Please drop this solution into an official answer.

And you have a solution :-) or should we say a workaround until the bug in grub 2.04 is squashed :-/