It is not as simple as you make it sound, because you are treating advanced technology like it exists in a vacuum instead of recognizing the physical cost of building it.

You call degrowth a trap, but ignoring physical limits is the real trap. Degrowth doesn't mean abandoning rail for inefficient small-scale production. It means intentionally shrinking the total material throughput of the economy. We can advance rail while drastically degrowing destructive sectors like aviation, the military, and industrial meat.

The problem is that building your advanced green infrastructure still requires massive mining for copper, concrete, and rare earth metals. Those mines destroy real ecosystems whether a socialist planner orders them or a capitalist does. Efficiency per person does not change the absolute physical footprint of extracting resources for 8 billion people. If your environmentalist socialism refuses to shrink our total material consumption, it will just plan its way into the same ecological collapse.

I think if it must be put simply, your communism is just vastly more optimistic than mine.