Now, your expectation is that Rufus can create an MS-DOS bootable USB if you provide your own version (as an ISO, or something else). As explained here, Rufus does not embed any version of MS-DOS with the application, so it doesn't matter what version of Rufus you use, you won't magically get a specific version but the Windows Millennium DOS version that Windows provides (that is, up to Windows 8.1, since Windows 10 removed it altogether, so there's no MS-DOS creation option in Rufus if running on Windows 10 or later).
