I have two screens connected to my pc:

• Main screen UHD (3840 x 2160)
• Secondary screen FHD (1920 x 1080)

In Control Panel, Appearance and Personalization, Display, the following options are set:

• Item size: 2 (next to smallest size)
• Let me choose one scaling level for all my displays: Off

When opening a windowed app in my main screen, the app is displayed correctly:

But after dragging this app to my secondary screen, the position of the controls within the app is off, it is not possible to control the app using the mouse and the ModernMix upper right corner-icon is displayed outside the screen.