[popoff]

As a matter of interest, I have also tried to get MobileSheets to open on a preset monitor with DisplayFusion.... and it doesn't work with that either, so I think Mike is right in assuming it is something within Microsoft's API. Other non-App store programs do work correctly with DisplayFusion.

What I do in the interim is to start MS with Full Screen mode off, drag or SHIFT WIN Arrow MS to the required monitor, then F11 for Full Screen.

Cheers
John

Hmmm, it seems that UWP has some limits over native apps. I tried displayfusion and it works for me, even in full screen.

You must to make a trigger with an action to move app to the second or third monitor. The trick is to use "C:\Windows\System32\ApplicationFrameHost.exe" as proccess name and "MobileSheets" as windows text. This is because all UWP apps run inside the ApplicationFrameHost and this is the proccess that you must to capture.

Regards.
Juan Antonio.