Some BIOSes have an annoying bug. If both a UEFI and a Legacy partition are present on the same USB boot drive, they will only present you with the option to boot from the UEFI partition.
To prove this, I suggest you rename the \EFI folder on the second partition of the Ventoy USB drive to say EFIxx. Then see if the BIOS lists the drive as a Legacy boot drive.
To prove this, I suggest you rename the \EFI folder on the second partition of the Ventoy USB drive to say EFIxx. Then see if the BIOS lists the drive as a Legacy boot drive.