To enable remote desktop in Ubuntu when “Settings” no longer shows the icon for “Desktop Sharing” or “Remote Desktop”, type:
$ vino-preferences
When your VNC client fails to connect with an error like “No matching security types” or “No security type suitable for RFB 3.3 supported” (or if you see a log line from vino-server like “Advertising security type 18”) then type:
$ gsettings set org.gnome.Vino require-encryption false
Then try to connect again.