Nextcloud with WebDAV on Synology NAS: No Gallery-Directory shown

I did setup a Nextcloud-Account on my SailfishOS-Device to perform manual Backups and share Pictures manually to my Synology NAS, which both is working. On my Synology NAS there isn´t installed any special Apps or Software for Owncloud-Support, so it seems it all works with the WebDAV-Connection to it.

I also add the path to my Pictures-Folder in Nextcloud-Settings but the Directory didn´t show up in Gallery-App. Sync is enabled to download to Device only all 15 Minutes, i did wait some Time but still no Nextcloud-Directory in Gallery.

What can be the cause?