Under Add-ons section you have to install File Editor and select option “Show in sidebar.”
It will appear on the left side in your menu.
I ran into trouble trying to use a full backup to migrate from a RPi3 to x86. My original system had a static IP and used DuckDNS. While attempting to restore the system from GUI(skipping creating the first user on the new blank install) it seemed to just sit there doing nothing for hours/days. I eventually did a reboot but could not access it at the IP address displayed on the connected monitor. It would ping. I ended up having to add the “s” to the URL and port number and satisfying the browsers security warnings, then I was able to access the system and log in. Example https://192.168.1.144:8123. Everything seamed to be there except for the static IP from the old system. I set the IP manually and now everything is working. Hope this helps.