Time for more wall demolition, this time in the basement.
The house was built in 1932 and the basement was remodeled for the first time in 1944.
The wall in question is about 11cm thick, made of masonry, and the floor above seems to be concrete slab (but I'm not sure). It also shares a window in a strange way as you can see in the drawing.
Attached is the drawing of the basement (which is not entirely accurate) and the floor above.