Comment 28 for bug 1429030

^ Please ignore my last comment, it still works just doesn't show grub menu and requires more patience before something useful appears on screen.

FWIW, i've created a script for downloading/unpacking mini.iso adding UEFI support

https://gist.github.com/pmartycz/74da258f6d876862b88caa9b4026b1c2

E.g.

$ ubuntu-mini-iso-uefi focal

Then you can just move files from focal/ to your FAT formatted boot media.