My guess is that as long as there is even tiny growth, central banks can react with negative interest rates/taxing cash. It will take quite a while until there is no growth at all on the whole world. I think even Western countries have room for growth by mandating green standards.

When less and less growth is possible any more, I imagine we would have to start socializing industries, which reached that point, so they are taken out of the equation. People would then get a basic income and use it to pay for state provided services, which would not deflate, because the state does not have to care about market prices, it can just regulate competition. I think the problem here is more to find the right time for it, not the solution itself.

That growth by population growth is not sustainable should be obvious, somebody in here made a good argument why this is true even if we populate the universe.