The only fix I can see is to have much better scenarios, or AI opponents, which I tend to think only the external communities around these games can produce. They generally don't allow that level of access for mods though.
Instead of scenarios or AI, why wouldn't it be the case that success invites more problems? You've got issues with immigration happening too rapidly for the population's taste, inflation devalues your accumulated resources at a more rapid pace, essential workers' pay isn't keeping up with FAANG, inequality is rampant, lots of homeless druggies appreciating your shelter & food bank infrastructure but locals are fed up, and also the next level up in government works against you out of envy or simple lack of appreciation for you contribution to the public purse. Power structures crumble because citizens get lazy and entitled, not knowing how good they have it, populism and self-interest rule the day.
Design success as the enemy of success, and you never run out of issues to solve. That said, it would be nice to see the winning endgame in real life for a change.
And a game almost everyone will hate, as it slaps you in the face and spits on you for succeeding.
Having a dynamic environment is one of the things that I've long wanted city sims to have. SimCity always had disasters, which is in the same vein, but they always felt like an afterthought (or a joke, in the case of alien or monster attacks). City simulations pretend to be serious flaw toys, so let me deal with a recession (or even a boom), or a dioxine contamination, or civil unrest. Not with a minigame, but let me deal with the city management aspects of those events.