If your E2B USB drive was happily UEFI-booting to the agFM menu system before, but now your BIOS refuses to UEFI-boot to it (e.g. it does not offer any option to UEFI-boot to any partition), then the usual reason is that you have accidentally caused an extra partition entry to be added to the E2B partition table.
This can sometimes happen if you are using .cfg or .grubfm files which use the ‘partnew‘ grub2 command and you have made a mistake in the menu code (perhaps not defined the filename of one of the files?).
The easiest way to fix it is to Legacy-boot to the E2B menu – if there is an extra partition added (usually partition 4) then E2B will warn you and allow you to delete it.
Most UEFI BIOSes require that the primary MBR partitions are in ascending order and do not overlap each other. If such an extra partition is added (with a non-zero type number), then the BIOS will ignore the whole disk!
Tip: You can use the Windows utility RMPrepUSB.exe to view the MBR partition table entries ( Drive Info – 0).