The main handle "hugs" the open window.
Legs inside the window and outside it clutch the window when you squeeze the handlebar. now you're cleaning device is locked in place. no suction or magnets.
of course it limits the pressure so you don't break the glass.
You set the angle for the rag by
turning the lever. pulling the arm towards you which pulls the rag towards the window. you control it up down and this way or that with the lever inside.
To move to another location you mechanically crawl along the window. the rags angle is independent of the legs angle making it easier to operate.
The exact mechanics are left to The experts.
If its too complicated to have one lever for both actions, the clutching action and the cleaning action then just make a second rag lever and have the rag lever go through a ring on the clutching device.