missing OEM apps from OnePlus like the camera

Not saying it's impossible, but it's probably very very challenging.

You can & should defo use commercial models for this, because it would be very expensive to have enough GPUs for a strong enough model if that's at all feasible.

I tested this with Claude just now. I uploaded my own compiled C program & asked Claude to answer questions about it based on machine code inference & it did figure out how scrollbar behavior works precisely, which it could not have inferred from the internet for sure. So I think if you have the tokens Claude can be used for this.

The problem is that you still need to roughly understand what you are doing, even if the LLM at the cost of hundreds of dollars can probably do 99% of the work.

My old TCL phone had the best IR blaster app I’ve ever used, and I’m missing that dearly, too!

That's probably something that can be vibecoded from scratch quite easily as long as you have enough screenshots of it & your phone actually has an IR blaster.