The --start-maximized option doesn't quite set the window to maximum size, but it is very close
What do you mean with this bit?
That parameter makes opera start in a maximized window and the only thing I see here, besides opera, is my bottom bar (panel).
I meant pretty much what I said. When I tried that option, the window was slightly smaller than it would have been if it were truly maximized, and, the icon on the window frame which when clicked is supposed to maximize the window, was still present on the frame, and when clicked, it did truly maximize the window.
However, for whatever reason, it sometimes seems to take a somewhat surprising amount of time for all the "background" processes associated with opera to stop. When I make sure that they have stopped before using the --start-maximized option, then the option has the desired affect. That's why I'm very glad that you made the point about closing opera completely. Even though the opera window was closed, your comment made me think about possible "background" processes.
I could be miss-recollecting, but I rather thought that quite some time ago, Opera was ostensibly built from purely hand-coded assembly language, and as such was impressively speedy. I'm still not sure how I feel about the more recent and "Chromium-ed" form of Opera.