Cubba27, good evening.
Notice that this is your first post here, welcome.
The Concrete looks like it was cast in the late WW2 era or shortly thereafter??
The images posted are really good, in one of them it appears that there is a solid piece of "something" in there it may be a packer of timber???
meaning that the roof structure was spanning the window opening, and to make up the gap between the window and the soffit of the concrete roof slab???
As for the spalled off concrete and the cement external patching, there is a very, very high probability that the face of the concrete above the window has been lost because of corrosion in the reinforcing bars embedded in the concrete roof slab.
Back in the day, it was not fully understood that the reinforcing had to be set back from the exposed surface of the concrete, if not the reinforcing would rust, the rust expanded and forced off the face of the concrete.
As for repair? all depends on how bad the area of missing concrete is, that area behind the cement render??
Can you come back and confirm what is directly above the window? is it a piece of timber?
Ken