Windows 10 - Different dpi text size settings per screen - How to detect?

All right, great. Then I would like to understand why you want to "detect" it. Is the problem is capturing the event of changing this system-wide property during application runtime? Anything else?

(By the way, "resolution", despite the wide use, by Microsoft (notoriously messing up terminology, sometimes to real serious confusion, like in case of "Unicode") and others, is a wrong term. This is just a size of screen in pixels. Resolution is related to the characteristic of system to resolve lines/points, measured in dots per mm/inch.)

—SA

Thank you for answering. Now, did I understand it right? Is the only issue when the user changes screen settings during your application runtime, or do you detect the screen size in the very beginning? Do you scale (not just resize) the application depending on that? You may think that what you are trying to do is obvious, but it's not. Most application don't try to maintain certain size of aspect ratio at all. You maximize window, and it takes appropriate size, the user resizes it, and it takes new size without any scaling; and still everything is shown fine, despite extremely low sizes, which can be limited. Essentially, from the very beginning, I was trying to ask what's wrong with this simple model, and what makes you designing something more complicated? Yes, I'm aware of different layout/scaling style where everything is measured in relative screen units. The goal is to maintain physical sized (in mm, not in pixels) for all elements on different hardware. Is that what you want to achieve? Something else?
—SA