Choice of screen savers on Apple tv 4th gen???

You can set your own photo based screen saver,

or you can select Apple-provided Aerial video clips as screen saver. Within the Aerials, you can select from four themes (any combination). Within those themes, you will be presented with randomized selection of clips from the categories (themes). I think the total is over 100 clips now.

Aerial screen savers on your Apple TV - Apple Support

Settings->General->Screen Saver->Type

Link->. Use Apple TV screen savers - Apple Support