- Start the presentation as normal so Screen 1 shows Presentation View and Screen 2 shows the presentation (F5 shortcut).
- On Screen 1's Presentation View, at the top of that view there is a drop down - 'Display Settings'
- Select 'Duplicate Slide Show'. It will now show both monitors as temporarily 'Extending'.
- Now you will see a small popup with an option to 'Resume Presentation', click this and the Presentation will now show in full screen on all connected monitors (I tested this with 2 additional monitors and this duplicated full screen to all 3).