Looks like digiKam is a bust, too. Auto-tagging is so bad as to be nearly worthless:
Reflecting pool in the fog? "traffic light"
Many photos of #Violet? "cat"
Drawing of a meerkat or someone spinning fire? "bird"
Box of rubber snakes? "bottle"
It's fairly good at *detecting* faces, but is totally unable to recognize them.
We might have to give up and stick with Google Photos because nothing else works.