Problem
There is no “Add (+)” button on the “Files” page of ownCloud as shown on the following screenshot:
Description
Since ownCloud 9.1 the “files” app providing this button is also using the WebDAV interface of ownCloud. If this WebDAV interface is broken (you might also get an “Your web server is not yet properly setup to allow files synchronization because the WebDAV interface seems to be broken.” in your admin backend) the button won’t show up.
Solutions
Please follow the link in the “Your web server is not yet properly setup to allow files synchronization because the WebDAV interface seems to be broken.” message to the documentation explaining the needed steps to make your environment compatible with ownCloud.
There is also an additional FAQ available here at central, giving you additional info: