How do I mount a Synology remote folder on iPad running iOS 13.3
Try connecting manually.  

In the top left portion of the screen, select the menu button at the top (three dots in a circle) and then select “Connect to Server”. Try using the IP address first.  Make sure you firm the URL correctly:

smb://&lt;Synology IP Address&gt;


You should be asked for username and password.

If that works, try it with the DNS name next.