I recently ran into an issue where my workspace is split in a weird manner. I probably accidentally pressed a wrong button, but I would like it to go back to normal full screen mode...
There seems to be no open window so I am not sure what exactly you want to achieve.
One can rotate through the Screen Modes by hitting F (at least by default).
One can also set the Scree Mode manually in the Toolbar.
This is a guess as I am a Windows user, but could it be the Mac Application Frame? You can turn it on and off from the Window menu.
Another thought is Overscroll in Preferences > Tools which affects how the document window behaves with Photoshop panels. I think the default is for it to be turned off, and things work much better with it turned on IMO.
Nice picture btw, and I love that whatever language your UI is using, spells words like Filter, Help and Plug-ins the same as in English.
This might illustrate the problem better. I can remember all the toolbars etc just being one big screen, but now everything floats independently.
Have you tried resetting the workspace? And is the Application Frame turned on?
I have tried resetting the workspace and that did not work. I am not sure if the application frame is turned on, how do I check this?
Window > Application Frame