In the common case: Boot Ventoy application via GRUB/EFI Ventoy EFI application scans the same drive it booted from with a vfat driver for disk images. Vento

In the common case: Boot Ventoy application via GRUB/EFI Ventoy EFI application scans the same drive it booted from with a vfat driver for disk images. Ventoy then creates chainload grub commands for every image it finds. You are presented a list of boot options, just like a normal grub boot. Selecting an option chainloads a boot from that disk image. There's devil in the details of course, but largely that's how it's working.