One problem is that in a world without major problems, stakes have to be low (which is perfectly fine and can make for an engaging story) or an external threat has to be introduced. The latter can easily feel forced or disconnected with the world.

I wonder how it would be to have a nonlinear game set in two time periods. One is a solarpunk-ish idyll under threat (with the protagonist's actions focused on protecting it) and the other is a preceding industrial dystopia (with the protagonist's actions focused on effecting change for the better).

Throughout the game the player first learns that the dystopian protagonist's actions did succeed in changing the world for the better but also that the threats faced by the idyllic period are consequences of those actions. The message is that even ideal decisions can have negative effects down the line, "happily ever after" endings don't really exist, and happiness requires maintenance. Yet, change for the better is both possible and worth the effort.

I'm right there with you on that one. For years I've dreamt about a post-apo game where you rebuild and look forward to the future, instead of wallowing in misery and barely getting by.
I think a 4X game, or better, something like a Heroes of Might & Magic might be the right scale to do it, but so far nobody seems to have seen the niche waiting to be filled. I dream of filling it myself but I simply don't have the energy for a project that scale. I'm no ConcernedApe or Tarn Adams, ha !

Tbh building settlements in fallout 4 felt a bit like that.