Comment 16 for bug 1846090

Sounds like it's maybe connected to a hardware multiplexer ("mux"). I don't have experience with such systems, but you might find it useful to look at these:

https://wiki.archlinux.org/index.php/Hybrid_graphics
\https://01.org/linuxgraphics/gfx-docs/drm/gpu/vga-switcheroo.html