Close a 7cm thick and 20cm deep groove in a load-bearing wall.

Fold hands and off to the structural engineer

Uh, no, behind. If I understand correctly, you chased out a cable from the opposite side of the wall. With such a clueless approach, I guess I don’t need to suggest that you illustrate your thread with schematic drawings. But maybe with photos?

When chasing out, I obviously took the side where the fuse box is also located. The suspicion was that the cable is also hidden on the inside wall side. Actually, it ran diagonally inside the wall. I have attached photos. The same again on another floor.

Why didn't you just make a new cut and not so deep!! I personally would have left the old cables in! Now the deal is done

Because I thought the cables were at the front. Then I was at it once. Yes, it would have been wiser to leave them in afterwards and

Hands together and off to the structural engineer

I had spoken with a mason. He said one could also rebuild it nicely with expanding mortar and the demolition of the stones. I would like to put that up for debate.

I would not rely on the expertise of a bricklayer. There is a reason why structural engineers have to study.

In particular, the third picture looks as if you wanted to cross-perforate the house with the angle grinder :-(

The same thing again on another floor.

Why not just open one surprise first?
Are you a humanities scholar, or where does this already remarkable zero to negative understanding of building anatomy come from?
Be sure to make videos of your work; you'll become a click billionaire within a few days, if not cause the internet to crash. That way you'll surpass any cycling singing kitten baby.