===== SOLUTION =====
Go ahead and read my problem statement, but look at my second post to see the solution.
Applications (a game in this case) have Property sheets.
"Properties" > _/Compatibility\_ > --Settings-- > [Change high DPI settings] opens a secondary dialog with the following controls:
[_] Use this setting...
[I signed in to Windows]
[I open this program]
High DPI scaling override
[_] Override high DPI...
I've tried all 12 combinations. They appear to do nothing.
I think these Property settings are meant to control graphic scaling, useful for high DPI systems. My laptop has a 3840x2160 display.
Can anyone tell me how to get 'Change high DPI settings' to work?