Everything sim. You start with, say, Sim City. You find that your rail network isn't working properly, so you switch contexts to a kind of Transport Tycoon style game, where you can optimise the train schedules and destinations. You realise that the factory you're delivering stuff to is struggling, so you switch context to a Factorio style optimisation game. You realise that the inputs to the factory aren't pure enough, so you switch context to an Opus Magnum/SpaceChem style atomic manipulation game. You zoom back out, and find that your hospitals are struggling too. Context switch to a Theme Hospital/Two Point Hospital style sim. You need medicines, so switch to a Big Pharma drug production sim. You can optimise the machines here with the same interface as you used for the factory. Zoom out a bit, and you can see a football stadium, with the option to switch to a football management game, or to jump into a game and start playing directly. You zoom out again, and are now looking at a country where your city/region is just one part. You can context switch to a country management game. Keep going out, and you realise you're on a planet, so start working on a space program. Keep going out, and you can build a Dyson swarm and get some interplanetary government vibes going, all while being able to zoom back in on any part.
Pretty sure my original concept was for this not to be a single game so much as a common interface for basically every other game, where unoptimised parts work, but aren't great, passing a kind of middle-of-the-range set of values whenever queried. By linking multiple games together, you'd be able to control everything.