Hello,
In my case connection ok with my credentials on Nextcloud storage with Let's Encrypt certificates but I can't access files getting "Error The attached file could not be found".

Debug D1978297891

This happens for any file. Here is a Debug ID when trying to download several PDF.

Debug ID D125912608

@houdiniL: Actually, you're just using linked files, not stored files. So this doesn't have anything to do with file syncing, which doesn't apply to linked files.

See above.