I use Multisystem at the installfest the trick is if you create it on a uefi machine it will only boot a uefi machine and only run Uefi iso's. if you build it on a non uefi machine it will only be able to boot a non-uefi configured machine but them will only install as non uefi
most uefi computers can be set to either but is a bit of a pain to switch a installed image between grub and grub-efi and adding a efi partition the redirecting efi bios to the efi-grub.
most newer computers are not uniform on how they implement UEFI so a bit of trial and error is needed. turn off secure boot and all uefi/efi options for non uefi installs and secure boot may need to be turned off for uefi installs.
to create images on usb I use dd for most iso's and ubuntu startup disk creator 18.04 up also works for most usb media creation.
to update the bios again each is a bit different. some i can update with a fat usb drive that has the new image on it others I have to a usb dos boot disk.
feel free to stop by the installfest on the 20th at UAT and I would be happy to assist and I have all the media ready to go to update bios and install most linux distro's