Ludwig Thank you for logs. There is indeed something strange going on. Probably this folder does on exist now, that is why there are errors accesing the files inside it and you can’t open it in Finder. However, it obviously existed at some point, that is why Tonfotos added it into the library.
The issue is, why Tonfotos cannot process the fact that is does not exist anymore. This looks like a bug.
Based on logs, there is something unusual happening. When program tries to access subfolders, it gets error code ENOENT - does not exist. However, when it tries to access /Volumes/Bilder NVME 4TB/.Trashes/501 - it gets error that it has no permissions to access it, and I guess this is what breaks the logic. If there would be ENOENT, probably it would disapper from the index already.
Still this all is not very clear for me. It would be great to see the output for the /Volumes/Bilder NVME 4TB/ folder, but I am afraid it is not in the logs. Can you please send me full logs from the moment app is started?