Question: Flickr share/upload stopped working
Suddenly I cannot upload photos to Flickr via share button in Photos. Regarding Flickr support forum, the problem in MacOS is caused by using an old authentication method, which was deprecated by Flickr. If that's true, it's an Apple problem and it needs to be fixed.
You can find more here: https://www.flickr.com/help/forum/en-us/72157664140017607/ .
MacBook Pro with Retina display, macOS High Sierra (10.13.3)