Modern UEFI BIOSes have either 32-bit UEFI firmware or 64-bit UEFI firmware.
64-bit UEFI can boot 64-bit Windows
32-bit UEFI can boot 32-bit Windows
99% of systems have 64-bit UEFI firmware.
It is not the same as the old legacy BIOS where a 64-bit processor could run both 32-bit and 64-bit Windows.
You can boot an MBR VHD containing Windows because the boot code works on both 32-bit and 64-bit BIOSes (because they both execute 16 bit code anyway), but UEFI firmware runs in different modes depending on if it is 32-bit or 64-bit and so the firmware must match the Windows bit-ness if you are UEFI-booting.
If your 32-bit Windows VHD is intended for legacy booting, then enable CSM mode in your BIOS and boot to Ventoy in legacy BIOS mode.
64-bit UEFI can boot 64-bit Windows
32-bit UEFI can boot 32-bit Windows
99% of systems have 64-bit UEFI firmware.
It is not the same as the old legacy BIOS where a 64-bit processor could run both 32-bit and 64-bit Windows.
You can boot an MBR VHD containing Windows because the boot code works on both 32-bit and 64-bit BIOSes (because they both execute 16 bit code anyway), but UEFI firmware runs in different modes depending on if it is 32-bit or 64-bit and so the firmware must match the Windows bit-ness if you are UEFI-booting.
If your 32-bit Windows VHD is intended for legacy booting, then enable CSM mode in your BIOS and boot to Ventoy in legacy BIOS mode.