My goodness, you’re not joking! I tried everything I could to make this work with the latest ISO, but it’s a no-go. I think you’ll have to resort to 20.0.1, or any hybrid-friendly version in order to boot and install, and then later update.
I’m going to try one extra trick and report back.
However, you still need to grab a copy of the minimal i686 ISO (32bit) of version 18.0.4 in order to acquire a copy of the file efi/boot/bootia32.efi and the folder boot/grub/i386-efi