I don't see AfD supporting debt brake reform, because they present themselves as fiscal hawks (and I reckon AfD wants CDU to fail so they can pick up voters from them).
But the Greens and whoever else should definitely negotiate with CDU for spending on vital infrastructure like electrical grid, rail, energy storage, etc. German economy is wrecked right now due to lack of demand, and Germany has excess industrial capacity to build out these physical investments that will pay off in the future.
Also sadly for Germany, if CDU fails, next election you might be looking at AfD led government like what happened in Netherlands.
I know it's needed, but I'm always worried about the French budget. Their debt to GDP is not healthy right now. On the other hand, the Germans should be spending more.