An ongoing issue with how Opera is framed on my desktop. First, I'm running Debian 'sid' with what I believe is its most default windowing environment: Gnome (49.1) with its Mutter window manager, a Wayland session, and 'adwaita' theme.
Long ago, Opera offered to frame its windows with the operating system / window manager's widgets, or Opera's own; but I can no longer find this option, so the only choice is 'Opera's own'; which means the window lacks normal widgets like 'close', 'minimize', etc. But it still has a drag handle area in the top bar (small bits of it, away from the various browser widgets).
The problem: subwindows also lack these widgets, and do not have a drag area. I am thinking particularly of the Inspector window, when it is detached from the browser window. It has no place to grab and drag.
So in sum: Linux:Gnome:Mutter:Wayland:Opera, detached Inspector window has no window manager widgets, particularly no drag area.