Use "Project" from the Action Center which is a win10 feature or desktop properties' display settings.
Looks like you can disable monitors @Screen resolution - drop down menu - another than main screen selected - which is extremely hard way to do and i cannot save these properties.
Catalyst had feature to create and save different display settings as quick launch icons to desktop which was very easy to use.
Bring it back
(Unless someone has trick to save windows screen settings as desktop commands)
PS. Not all games support 3 displays especially old ones.