legacy and uefi use different boot loaders so a usb made for uefi will only boot with uefi,you will have to make a USB with mbr boot loader to get it to start on legacy bios.
legacy and uefi use different boot loaders so a usb made for uefi will only boot with uefi,you will have to make a USB with mbr boot loader to get it to start on legacy bios.