I loaded up the 100k city and it was playable after following the various guides out there for me. It reminded me a bit of how Dwarf Fortress used to slow down and stutter when you had a lot of dwarfs running around.

That said, they should have kept it in the oven until sometime in 2024. Besides performance improvements there are a few rough edges especially Chirper and in the simulation itself that need more work. One example is civs complaining about healthcare excessively until you unlock the upgrade for the full hospital and build one. Also some of the new tools like the road one and the pipe system need more polish as they can be unintuitive and frustrating to use at times.

It's ultimately not a bad game it just shouldn't be released yet. They should have gone the early access route because that's how it feels at the moment.