SUMMARY Some GTK apps, when right-clicked on the title bar, don't offer the option to move to a different virtual desktop. STEPS TO REPRODUCE 1. Setup several virtual desktops. 2. Launch Peek (https://github.com/phw/peek). 3. Right-click peek's title bar. OBSERVED RESULT There's no option to move to a different desktop. EXPECTED RESULT Should have an option to move to a different desktop. (Using KDE plasma 5.17.5, in debian testing)
Peek is a GTK3 app that uses client-side decorations; it draws its own titlebar rather than letting KWin draw it. As a result, you don't see the context menu, since it's provided by KWin. No KWin-drawn titlebar means no KWin-provided context menu. I'm afraid this is simply one of the drawbacks of apps that use client-side decorations.