Seems like gnome-photos expect the flickr plugins from media-plugins/grilo-plugins. gnome-photos: [registry] ../grilo-0.3.14/src/grl-registry.c:1523: Plugin 'grl-flickr' not available gnome-photos: Unable to activate Grilo's Flickr plugin: Plugin “grl-flickr” not available
Missed a line... gnome-photos: Unable to fetch the list of available renderers: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name is not activatable
Re-emerging media-plugins/grilo-plugins with the flickr USE flag, fixes the problem. Will send PR.
I saw out that gnome-photos does have a flicker USE flag, which will automatically pull in the grilo flickr plugin. I can also see there are a few extra dependencies on adding the flickr USE flag. So it makes sense it isn't enabled by default. However, it might be worth considering giving a warning to users that having the flicker USE flag may cause this expected trivial warning. From what I can see, it doesn't affect the program other than the obvious.