Styles work (and worked) differently depending whether they're used as system ones or SAB styles (you're not supposed to place them there but everybody did). You have to figure out how to shove StartPanelComposited into style set for the system.
Maybe you're in dark mode? Because IDM uses custom dark mode. Is window context menu acrylic?
Or maybe you're not admin and it's elevated? Or hidden from taskbar? Observe DebugView output when launching app.