That also means massive unemployment

Good idea! Let's just replace workers with robots straight away and they can live work free!

How would business work? Currently a business's purpose by law is to make money. How would you enforce a different goal without going full centralized economy?

And how is trying to add less value more effective than internalizing externalized costs? For example, co2 is an externalized cost, one companies don't need to pay for right now, it's external to them. If we made them pay for it to fund carbon capture at 1 ton removed for every 1 ton emitted, they would decrease their emissions and the rest would be removed. You could do something similar for other ecological issues as well. What's the benefit of degroth over internalizing costs?