if we 100% stop having kids, sure. but how about slowly reducing to a total world steady state population of 1 billion. Will that necessarily lead to collapse?

if we 100% stop having kids, sure. but how about slowly reducing to a total world steady state population of 1 billion. Will that necessarily lead to collapse? maybe with that many people a shift to fossil fuels would t matter so much. maybe we could all have good sized homes and yachts.