If I run a setup application (installer) then if I move the installer window on the second screen the button remains on the first taskbar, there is no button on the second taskbar even though the window is on the second monitor.
This happens for any program that is "Run as Administrator" not just installers. Dual Monitor can't touch these windows unless you also run it with administrative rights. If you right click on Dual Monitor and start it by clicking "Run as administrator" then it will do what you want.
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Yes, you are right. I just tried it to run it as an admin and in this case it works.
Unfortunately if I check it to run as an admin it does not autostart with Windows.
There must be a way to solve this without admin privileges since other taskbar managers did it (Display Fusion for example)