@myswtest You are showing the main window, in which the developer tool is docked. Click the ... button on the top-right and make it a separate window.

Also, if you are using KDE, this problem may not exist, because, if I know it correctly, KDE supports server-side decoration. Gnome does not support it, so Wayland applications need to provide the window title bar on its own.

Under Wayland Gnome, currenty Opera shows no window decoration for the developer tools window, if Opera is running as native Wayland app. I have tried other Chromium-based browsers, and they all had custom window decoration, so Opera is the only browser that has this problem.

Fix this. Add a client-side decoration, like Opera's main window.

Opera

Vivaldi

Chrome