Maybe someone here in the forum has a brilliant idea?
Brilliant, I don't know, but this could work
The window as a double sash, but both able to open, with a glass partition in the middle of the sashes. The glass partition can be attached and sealed to the middle post of the window in the reveal using an additional aluminum profile or similar. Drywall with tiles could also work here. Window for opening to improve ventilation, not fixed glazing. The gap between the sashes, where the post is visible and accessible, basically only allows a narrow profile or a glass pane. You can get around this by using two separate windows instead of a double sash window and a coupling profile in the middle. That makes working there much easier.
About 70 cm remain for the toilet from approx. 90 cm for the shower. Not a palace, but quite usable for people of average build. The pre-wall element would have to be extra narrow so that the toilet is centered (I assume the drain goes right through to the ceiling). Washbasin at the entrance and change the door hinge to open outwards.