T430 BIOS Downgrade: USB visible in F12 menu but won't boot (auto-1vyprep)

ing to downgrade my ThinkPad T430 BIOS to v2.60 to use 1vyrain. I'm stuck at the very first step and could use some help.

The Problem: I've generated the winflash.iso using the auto-1vyprep Docker tool on Kali Linux. When I plug the USB into the T430 and press F12, the "Generic USB Flash Disk" appears in the Boot Menu. However, when I select it and press Enter, the screen just refreshes or ignores the command and it won't boot into the WinPE environment.

What I've tried so far:

• BIOS Settings:
  • Flash BIOS Updating by End-Users: Enabled.
  • Secure RollBack Prevention: Disabled.
  • Secure Boot: Disabled.
  • UEFI/Legacy Boot: Tried "Both", "UEFI Only", and "Legacy Only".
• USB Creation:
  • Used dd with conv=fsync.
  • Tried manual FAT32 formatting and copying files.
  • Tried different USB ports (right-side 2.0 and rear port).
• Hardware: Running with AC adapter plugged in.

My Current BIOS Version: 2.7x (Locked version).

Is there a specific quirk with the T430 and WinPE-based boot USBs? Should I be using a specific partition scheme (MBR vs GPT) for auto-1vyprep to be recognized? Any advice is appreciated.