Locking video source when casting via AirPlay

I would like to know how to lock my video source when using AirPlay so that it’s a dedicated video source.

Quite often, when I’m streaming a video to my TV (via my older Apple TV) that doesn’t need my constant attention, like a lecture, I’ll inevitably switch to another site (The NY Times, Amazon, Reddit, etc) on my device (usually my iPhone), and visual elements and videos from those websites will cast via AirPlay, onto my TV. This is super frustrating, especially when I don’t even trigger these elements to play. Aside from using another device for surfing, how can I prevent this?

If Apple doesn’t have a solution for this, are their 3rd party apps that will correct this issue? -Thanks.