Every UI framework that runs on Windows has to communicate using Win32 API at the lowest level. Here is the guide: https://learn.microsoft.com/en-us/windows/win32/hidpi/high-d...

Every GUI application on Windows runs an infinite event loop. In that loop you handle messages like [WM_INPUT](https://learn.microsoft.com/en-us/windows/win32/inputdev/wm-...). With Windows 8, Microsoft added a new message type: [WM_DPICHANGED](https://learn.microsoft.com/en-us/windows/win32/hidpi/wm-dpi...). To not break the existing applications with an unknown message, Windows requires the applications to opt-in. The application needs to report its DPI awareness using the function [SetProcessDpiAwareness](https://learn.microsoft.com/en-us/windows/win32/api/shellsca...). The setting of the DPI awareness state can also be done by attaching an XML manifest file to the .exe file.

With the message Windows not only provides the exact DPI to render the Window contents for the display but also the size of the window rectangle for the perfect pixel alignment and to prevent weird behavior while switching displays. After receiving the DPI, it is up to application to draw things at that DPI however it desires. The OS has no direct access to dictate how it is drawn but it does provide lots of helper libraries and functions for font rendering and for classic Windows UI elements.

If the application is using a Microsoft-implemented .NET UX library (WinForms, WPF or UWP), Microsoft has already implemented the redrawing functions. You only need to include manifest file into the .exe resources.

After all of this implementation, why does one get blurry apps? Because those applications don't opt in to handle WM_DPICHANGED. So, the only option that's left for Windows is to let the application to draw itself at the default DPI and then stretch its image. Windows will map the input messages to the default DPI pixel positions.

Microsoft does provide a half way between a fully DPI aware app and an unaware app, if the app uses the old Windows resource files to store the UI in the .exe resources. Since those apps are guaranteed to use Windows standard UI elements, Windows can intercept the drawing functions and at least draw the standard controls with the correct DPI. That's called "system aware". Since it is intercepting the application's way of drawing, it may result in weird UI bugs though.