First, we don't need fusion power as a "solution". All that would do is extend over-populating by virtue of Jevon's paradox, as humanity doesn't plan ahead re resource consumption vs. preservation any better than fruit flies.
With an electrified grid powered by solar, wind, backed up by batteries, more use of public transport, etc., suburbs don't have to become wastelands. But living standards and especially habits re wastefulness will have to change over time.
Living cheek to jowl does NOT seem at all fun. But good luck getting humans to procreate less, or agree on policies to encourage that, unless they are forced to by, say, mother nature killing of a large proportion of the masses over time, due to population induced (and obvious) consequences of endlessly growing the population as a "normal" behavior.
It still strikes me as odd how unusual it is for people, even in the "educated" first world to choose not to have children. Even with how obvious the downsides are for humanity, re continuing overpopulation. I suppose people just ignore what they don't want to hear, and can continue to blame "everyone else", as long as they get to do what they want in the short term.
Disclosure: I chose not to have kids -- I chose instead to help neices and nephews get educated, make more balanced decisions, etc. One doesn't have to "hate children" to choose not to have them in the modern era.
Given the track record of the perma-doomer blogs, I wouldn't bet a fast crash doomer's money on their predictions.