Can you export a screen saver slide show?
Title IS my question
Question marked as
Yes, with iPhoto v9.6.1 on High Sierra, but not with Photos on any release of macOS, including Big Sur 11.1.
In Photos, you can construct a slideshow via the instructions on Export photos, videos, and slideshows from Photos on Mac, but that .m4v slideshow movie is not selectable in the Desktop & Screen Saver Preference panel. I just tested this on Big Sur 11.1. You can double-click on that Photos exported slideshow, and Apple TV will play it.