IIRC, it used a filesystem driver shim that rerouted all FS writes during installation into an overlay filesystem image; and then generated a self-unpacking executable, embedding that overlay image, that unpacked the core EXE and spawned it shimmed to read from the overlay image.
What did Windows 10X do that was different than that?
a lot of things work just fine and are still failures from the management's point-of-view