eglfs talks to the system's framebuffer, which does not have support for windows.
You need a windowing system to do that, e.g. X11 or Wayland.
Not Qt specific of course, that is a system setup thing.
Not sure what that has to do with multiple windows. A QStackedWidget is never multiple windows, it is one widget showing one of many pages.
Cheers,
_
Bookmarks