Similar project of mine that connects a phone to a PC browser using a WebRTC QR code so you can use a pen / touch on the phone to create drawings on the desktop:

https://www.youtube.com/watch?v=Gvsm84xL9Sk (https://github.com/phiresky/webrtc-remote-touch-pen-input)

Sadly it needs a (tiny) server component to exchange the initial connection information - using a QR code in both directions is smart, but also pretty annoying for the user.