Just as a point of Windows philosophical reference; in a person-to-person forum like this, one should never recommend sending a user (God knows who) into the registry to make changes of any kind!
That said,
I don't mind being a limited tester for things like this; part of my career path for decades as a software engineer. I followed your instructions to the letter, including the registry edit required to change the high DPI scaling override (mine were greyed out). I changed the the override for RealFlight as instructed to 'System(enhanced)'. I restarted the system.
The report is that 'System(enhanced)' did not change the scaling in RealFlight9 in any way... all menus, screens, toolbars, and dropdowns are still very very tiny. My external display (on NVidia GeForce GTX 1660 Ti) is 2560 x 1080 100.002 Hz (Windows 10; latest patches, etc)
PS any thoughts ?
marcus