Here's a question about screen sharing

The concept of sharing a screen is to easily capture the screen and send it to the other person. In fact, the remote desktop we use also captures and sends the screen.(Of course, you're supposed to use an effective algorithm to send only the parts that change.)

The part where the image stream is exchanged can be bypassed by the nat problem and can be managed centrally with the stun server in the middle. You can use html5's canvas and websockets.

However, the problem is that screen capture is a system area independent of the web. (The BitBlt function is typical in Windows.) It's not something you can solve in your browser, but something you need to solve in Windows. Therefore, you must deploy Activex or a separate program to control the system.