There can be many reasons why a computer does not boot from USB. In your case it boots in UEFI mode, but not in legacy alias BIOS mode.
I need more details in order to help you solve the problem.
- What computer is it (brand name and model)? I know that some HP computers want an MSDOS partition table to boot from grub in BIOS mode. You can select that in the settings menu of mkusb-dus.
There can be many reasons why a computer does not boot from USB. In your case it boots in UEFI mode, but not in legacy alias BIOS mode.
I need more details in order to help you solve the problem.
- What computer is it (brand name and model)? I know that some HP computers want an MSDOS partition table to boot from grub in BIOS mode. You can select that in the settings menu of mkusb-dus.