Apple TV
With the Apple TV box, what are the built in apps?
Apple TV 4K
The default apps depend on the generation of the model and the country or region.
There are handful of default apps, as developed by Apple, on a new Apple TV (4th generation or later). Some apps depend on the country or region of the Apple ID that is entered during setup, i.e. apps for unavailable services are not installed.
The user is supposed to get additional apps from the on-device App Store, similar to how it works on a smart phone. Some App Store apps are free with free content, some apps are free with subscription content, and some apps require a one time purchase.
The screenshots on this support page give a good impression of the 11 default apps, with some user-installed additional apps in a user-defined folder (12th icon on the home screen).