Hadn’t noticed this earlier but when the box first came out the Chromecast couldn’t be configured to set the “ambient” screensaver mode where photos from Google photos could be streamed as a backdrop.
That has been enabled now so I can watch photos of my kids when the screen isn’t in use. Nice!
It seems to have a mind of its own, and think this is a Google rather than an aura issue from reading other forums. The photos option reappears sporadically with a bit of trial and error.