Download:
- Windows 11 ISO
- Ventoy
- Ventoy VHD boot template
- VirtualBox (portable)
- Rufus (portable)

Diskpart:
Create and mount 50GB VHD

diskpart
create vdisk file=c:\win11.vhd maximum=51200
select vdisk file=c:\win11.vhd
attach vdisk

Rufus:
Write Windows 11 ISO as Windows To Go image (GPT and UEFI) to the VHD.

Diskpart:
Unmount 50GB VHD

detach vdisk

VirtualBox:
Create a Windows 10 VM with the existing c:\win11.vhd.
Change VM Settings > System > Motherboard > Enable EFI.
Boot until language selection and shutdown VM.

Ventoy:
In Ventoy choose Option > Partition Style > GPT.
Under Device choose your USB-drive and click Install.

Explorer:
Manual format the created Ventoy partition as NTFS.
Place win11.vhd on your NTFS formatted Ventoy partition.
Place ventoy_vhdboot.img in ventoy folder on Ventoy partition.