I'm not sure if I'm just crazy but I distinctly remember being able to send touch input to a game that I'm playing over the Steam Link app a few years ago. It wasn't simulating a mouse but was behaving as if the computer itself had a touchscreen interface.
However, I can't figure out how to do that now with the current Steam Link app for Android. I wanted to try out a game's touch input support but my computer does not have a touch screen so I was hoping I could simulate it by streaming the game over Steam Link and then doing the touching on my phone but I can't find a way to do it. It will only either simulate a gamepad or the mouse. No touch.