Apple says "If you're using an external USB hub with several connected USB devices, the external USB storage device you wish to start from may not be recognized, or, may need to be connected directly into one of the computers USB ports instead. Some computer keyboards that include USB ports may not supply enough power to some external USB hard drives."
Could you tell us which partitioning tool you are using to partition this disk? Windows Disk Management tool or other third-party partitioning tool? We recommend using built-in Windows Disk Management to partition the disk.
In theory, as long as there is a FAT32 partition on a GPT disk, then the disk will appear as a EFI boot option.
Could you tell us which partitioning tool you are using to partition this disk? Windows Disk Management tool or other third-party partitioning tool? We recommend using built-in Windows Disk Management to partition the disk.
In theory, as long as there is a FAT32 partition on a GPT disk, then the disk will appear as a EFI boot option.