Can’t updated photos onto AppleTV

You don’t need to turn home sharing off and on, you just need to go back into settings and select home sharing again for the screensaver so it can cache a new batch of photos. The screensaver isn’t going to update on its own and it needs access to the computer to access home sharing, so it will require that to flush and sync a new batch.

For photos on your Mac, use Home Sharing and the Computers app.

For photos in iCloud, use the Photos app.

For screen saver photo collections, these are cached when activated, and do not update until you reset the screen saver.

It's dependent on what you want to use. Home Sharing would be using your local library from your computer (which would need to remain on in order to access the content while it syncs over), while Photos would be accessing your iCloud library.

You can only select an album for a screensaver, and it's only going to sync a certain amount (typically a few hundred). It will remain until you select the option again so it can be flushed sync a new batch. If you want to view more photos then you can manually start a slideshow.

For photos from your Mac or PC, turn Home Sharing off and on.

For photos from iCloud, go to the album or stream in the Photos app, and set your selection again as screen saver.

You would go into settings - general - screensaver and selecting home sharing as the type, which will sync a new batch.