I'd like to boot a live USB for FreeBSD 11.1 in my UEFI firmware. I tried creating a live USB using:
dd if=FreeBSD-11.1-RELEASE-amd64-dvd1.iso of=/dev/sdc bs=4M status=progress && sync
Then I tried booting this USB and I got the GRUB message:
error: unknown filesystem. Entering rescue mode. grub rescue>
There's nothing wrong with this USB as I've managed to boot several distros from it and not that long ago (a month at most was the last time I did), with me placing those distros on the USB using much the same dd command.
I'm running Arch Linux and I do not have Windows, macOS or any non-Linux operating system installed so if your method involves using another operating system I'm afraid it is not applicable.