Macbook Pro on but display is blank
I realized that the display was on but extremely faint (could barely make out some lines).

It’s your video mux and your back light.
This is a telltale symptom that your back light is out. However, you have additional symptoms, that compound this problem.
The LED back light is exactly what it sounds like - it's the light behind the LCD that makes what’s on it visible.  It could be the light itself, the fuse, or any of the electronic circuity that handles it.
Now, the video mux (multiplexer) is a chip that handles the “switching” of the video signal between the internal and external displays and where applicable the integrated and discrete video adapters.
This may be a coincidence or it could be some common components that have failed.  Either way, this is not a DIY fix - it’s something you’ll have to take it in for service.