I've noticed when I use the DisplayFusion context menu to "Load next Wallpaper..." I get a windows toast notification telling me I've done so. I find it distracting, but can't seem to find an option to do so...

If you want to turn off all toast notifications with Windows 10 then press the Winkey + i to open the Settings app.
Click on System then on Notifications and Actions.
Under Notifications there is a switch: Get notifications from apps and other senders, switch that to off and you shouldnt get anymore toast notifications.