Mostly yes, it works all at the same time.
It depends on what services might be used simultaneously.
Up to 6 streams of Apple TV+ content can be streamed simultaneously.
For Apple TV app Channels, most Channels allow 3 simultaneous streams.
For iTunes Store purchased movies, at least two streams of the same movie can be played simultaneously.
For iTunes Store rented movie, one stream of that rental can be played at one time.
For Netflix, it depend on your plan (1/2/4 screens).
For Disney+, 4 simultaneous streams are allowed.
For Hulu, users are allowed 2 screens, or unlimited screens with an add-on.
For Amazon Prime Video, 3 streams are allowed simultaneously.
For other services, please check their websites.