[Bug]: exfat option in Make2023BootableMedia.ps1 results in non-bootable USB

Is there an existing issue for this?

• I have searched existing issues

Current Behavior

Using -FileSystem ExFAT when attempting to make a bootable USB results in a non-bootable USB. This seems to happen because most UEFI firmware does not support ExFAT by default.
Although FAT32 is the default, it doesn't work for larger partitions and the script recommends to use ExFAT in that case.

Expected Behavior

Using the script should result in a bootable drive, so the ExFAT option should not exist unless there is some way to make it bootable on most computers.

Steps To Reproduce

1. Tested with Windows 11 with Secure Boot enabled and updates applied, using a 256 GB USB stick with a GPT partition table and a single partition covering the whole drive. The ISO used was Win11_25H2_English_x64_v2.iso.
2. Run .\Make2023BootableMedia.ps1 -MediaPath C:\Media\Win11_25H2_English_x64_v2.iso -TargetType USB -USBDrive E: -FileSystem ExFAT (adjusting the command to point to the correct paths). The script should not display any errors at this stage.
3. Attempting to boot from the USB will likely fail as UEFI firmware is not required to understand ExFAT.

Build Environment

- OS: Microsoft Windows [Version 10.0.26100.8457]
Bug report is for a script, so I didn't build/compile anything, just downloaded it.

Version Information

Tag: v1.6.4-signed

Urgency

Low

Are you going to fix this?

Someone else needs to fix it

Do you need maintainer feedback?

No maintainer feedback needed

Anything else?

There is a message in the script saying that the filesystem must be FAT32 to boot on most UEFI systems but the actual code still allows ExFAT so that error will never actually display if -FileSystem ExFAT is used.

Log:

.\Make2023BootableMedia.ps1 -MediaPath C:\Media\Win11_25H2_English_x64_v2.iso -TargetType USB -USBDrive E: -FileSystem ExFAT


Microsoft 'Windows UEFI CA 2023' Media Update Script - Version 1.4


WARNING: Contents on drive [E:] will be erased! Continue? (Y/N)
y
Initializing staging directory
Staging media
Mounting ISO from staged media
Mounting boot.wim from staged media
Updating staged media to use boot binaries signed with 'Windows UEFI CA 2023' certificate
Creating 'Windows UEFI CA 2023' bootable USB media on drive [E:]
Successfully created media on drive [E:]

Start with Make2023BootableMedia.ps1 and reproduce the reported command using -FileSystem ExFAT. Inspect the filesystem validation and the existing FAT32/UEFI warning, then verify that the resulting behavior matches the documented bootability requirements. Done means ExFAT is handled consistently with the script’s UEFI guidance and the issue’s reproduction no longer produces misleading success.