This seems to be a noted problem on the Apple community, with posts going back years without a solution.
I have been able to set up the screensaver on my AppleTVs (4K, latest OS) to use my recent photos from homesharing or from Photos. But once set up, it never updates the photos. Is there a way to have it frequently updated to my most recent photos (or even better, a random selection of all my photos)?
Apple TV 4K, tvOS 15
You would have to go through the steps to set a screensaver each time you want a new batch displayed, this can be done through the Photos app if you are using Photos from your iCloud library.
Create a photo screen saver on Apple TV - Apple Support (CA)
If it done through Home Sharing then you need to go into settings to select that type and the associated computer would need to be running while it goes through the caching process.
If you want to view a larger set of photos you choose to start a slideshow instead.
Create a slideshow on Apple TV - Apple Support (CA)
Photo screen savers are cached on (copied to) the Apple TV disk. The way it currently works, is that the photo collection is fixed from the moment it is set. To update with new photos, you will have to set it again.
To view other photo sets/streams/selections each time, use the app instead of the screen saver.
Which app? Photos?
And I’ve tried selecting other screensavers (often then rebooted the AppleTV), then select homesharing again, to not have the photos updated.
Updating homesharing photos screensaver on AppleTV
