Maybe this old news, but I haven't seen it done yet. I was excited to hear Assistant is coming to Android and wanted to try this out.
Seems to work with any cast enabled app. Not just YouTube or Netflix. Google Home can control any media casted as just can't initiate it.
Edit: Trigger Warning
omg I was watching that youtube video and my Google Home is next to me. She was trying to do those commands as the guy was saying them. Had to quickly turn the mic off.