Closing and opening the project doesn’t work, and i can’t dock anything with it. If i minimise it the whole program minimises. same for closing.
That looks like the main frame for the editor. You should be able to reset your layout to get rid of it - Why is there a window behind the Editor? - Platform & Builds - Epic Developer Community Forums
One little hack that seems to work for now is closing and opening the level blueprint, it will often snap into this blank window. then you should move everything else INTO that window. trying to grab it out again will leave you with the same situation.
OK scratch that, by far the best way is to go Window > Reset Layout.