thank your very much for your help. unfortunately i couldn't test it - i did a reinstall in the morning. the german chat-support couldn't help me ... so i had to make a reinstall .. all my libraries are gone.. so bad.
Sorry for the inconvenience caused. Are you able to locate the catalog or its backup following the steps mentioned in Recover catalog and images after resetting preferences in Adobe Photoshop Lightroom
Wir sprechen hier auch Deutsch wenn das was hilft
Die Neu-Installation entfernt niemals die Kataloge. Suche auf Deinem Drive nach *.lrcat Dateien.