No lintel, so the brickwork dropped
There was never a lintel here in the first place. Without one, there's nothing to carry the brickwork over the opening — so over the years it did the only thing it could do, and dropped.
You can see the cracking and the movement in the first photo. The wall was supported, new lintels were installed to take the load the way it should have been taken from day one, and the brickwork was rebuilt above them.
It's not a glamorous job. It's the sort of thing that stops a small problem becoming a very expensive one.