mediathek schliessen
After starting 'Photos' I get the message 'mediathek schliessen' ('close mediathek'). But I do not know which mediathek. Perhaps I renamed the last mediathek some days ago and cannot remember its name.
iMac 21.5″, macOS 10.14
The message is stating that Photos is closing the Photos Library . If it does not finish for a long time use the > Force Quit (Sofort beenden) dialog to quit Photos.