The automatic backup of enpass cannot change the location of the backup.  I selected the device (Synology) on the local network.  The prompt: The current location cannot be accessed.  However, this device is accessible, and this device is the device for webdav synchronization.

To change the backup location in Enpass, you'll need to install the website version of Enpass, as the store version does not allow for location changes.

Once you have the website version installed, you should be able to set your Synology device as the backup location without any issues.