https://techcrunch.com/2020/09/14/facebook-introduces-a-co-viewing-experience-in-messenger-watch-together/

Facebook today is rolling out a new feature that will allow friends and family to watch videos together over Messenger. The feature, called “Watch Together,” works with all Facebook Watch video content, including its original programs, user uploads, creator content, live streams, and soon, music videos. At launch, the co-watching experience can be used by up to 8 people in a Messenger video chat on mobile, or by up to 50 people in Messenger Rooms.

The COVID-19 pandemic has encouraged a number of streaming services — including Hulu, Plex and Amazon Video — adopt similar co-viewing features, or at the very least, unofficially permit third-party apps that enable co-watching, like Netflix Party.