MakePartImage v106 now available (Ubuntu bug fix for .imgPTN23 files)
It seems that hybrid Linux ISOs now legacy boot via a \boot\grub\i386-pc\eltorito.img file. This file can legacy boot if the hybrid ISO is dd'd onto a USB drive, however it will not boot successfully if you merely extract the files from the ISO and copy those to a standard MBR USB drive. E2B can boot from the ISO directly however, but if you make a .imgPTN23 file from the ISO (e.g. Ubuntu or XUbuntu) then the CSM legacy menu would not be able to successfully legacy boot using the standard grub4dos menu in the CSM menu.
Rufus seems to have to work around this issue by offering two 'burn' choices, either:
a) a dd mode where the hybrid ISO is imaged onto the USB drive - OR
b) a file copy mode where Rufus extracts the files from the ISO onto a standard MBR /GPT partitioned USB drive and then adds Syslinux and creates a syslinux cfg file to allow a vmlinuz and initrd file to be loaded using syslinux commands (because the eltorito.img boot file inside the ISO does not support standard disks).
I have now updated MakePartImage so that it should now be capable of legacy booting Ubuntu and XUbuntu and perhaps some other 'casper' based Linuxes using the first standard boot option.
So if you are having legacy boot issues with .imgPTN files, try remaking the file using the latest (106) version from Fosshub.
https://www.fosshub.com/Easy2Boot.html