I have tried dragging the corner of the frame into the other frame to close it… nothing.
I have tried right-clicking where the two frames join and choosing “Join Frames”… nada.
How do I get rid of that window? It’s driving me crazy.
It’s the default layout which has 5 editors. The top one is info editor but you usually only see the bottom of it which acts as a top header. You’ve dragged the top header down. If you want to get rid of it, editors you’re joining has to have matching shared edge. In this case you could split the info editor to have edges for joining with the 3D view and with outliner and then join them up.
But you probably want to keep the top header where it is so just drag it back up.