Matthew Garrett wrote about this, about a decade ago. It turns out you can create an iso/usb hybrid image that boots correctly on all combinations of BIOS/UEFI, optical disc/usb drive, and PC/Mac.

https://mjg59.dreamwidth.org/4957.html

Dreamcast uses El Torito for booting as well, I bet you could make that work too. Possible issues are that I don't know if the Dreamcast will inspect multiple boot images to find an appropriately labeled one, and I don't know if the other platforms will accept a bootable disc that's prepared for Dreamcast (must have at least two sessions, first session audio, second session data with el torito for booting)

https://wiki.syslinux.org/wiki/index.php?title=Isohybrid https://repo.or.cz/syslinux.git/blob/HEAD:/utils/isohybrid.c