Other studios' trailers and clips, that is, like this one for Alec Baldwin's Drunk Parents:
From Ryan Christoffel's "Apple Launches Dedicated YouTube Channel for Apple TV" posted Tuesday on MacStories:
Over the last few weeks Apple has quietly debuted a new YouTube channel dedicated to one of its services: Apple TV. The Apple TV channel is home to a variety of videos, like trailers for upcoming films and TV shows, exclusive behind the scenes clips and interviews tied to popular shows and movies, and, of course, videos highlighting Apple's own original content efforts, like an Apple TV+ trailer and Carpool Karaoke previews...
The channel [has] an odd, yet interesting relationship with Apple's own TV app. While the channel serves to promote the Apple TV service, its videos by and large aren't available on that service's app. The behind the scenes clips and interviews found on this new channel are not currently available in the Apple TV app, only on YouTube – though it's certainly possible that will change in the future. Similarly, most of the trailers on YouTube are unavailable in the TV app, since unreleased films and shows don't exist in TV's content database.
My take: Apple is usually pretty good at rolling out its new stuff. This is weird.