[...] The single screen size is selected. [...] Ideas?
Hello!
This is the standard behaviour for some versions already. One window is enough.
If you want other dockable windows (Dialogs), go to
Windows, select
Dockable Dialogs then
Tool Options.
For years, this was the default window so I guess this was the "missing" one. Obviously, you can open any of the other dialogs repeating the same steps.
However, remember that only the opened dialogs will show next time. If you close them and then close GIMP, it will start again with the image editor window.
Good luck!
