A problem that was bugging me when trying to install Linux to USB was an error like:
64 bit OS not found
Even if partitioning everything perfectly fine, Debian Stable Net Install may fail if installing to USB, and this may include other distros as well, such as Linux Mint.
The EFI may not be able to be done correctly, so swap it out.
Using a live session of Linux Mint, I was able to transplant a working EFI into the USB with gnome-disks and proceed to boot with the USB.
If the EFI is broken, swap it out with something that works.
- sudo gnome-disks for root privilages when modifying partitions in a friendly GUI
- Create partition image of EFI from a working existing install and save it in your live session file system
- Restore that newly created partition image in the USB’s EFI partition. (or delete the broken EFI and place the EFI partition image in free space)
Bug me and I may include images if needed