I'm assuming that its something to do with the tracking of every citizen and their lives or something. Thats a new feature in CS2 , mind you its also the unity engine, which doesnt run the best as it is, it often doesnt make the best use of multicore
In the various streams that I've watched I have seen various configs, 16gb, 32gb, AMD, Intel, everything from a 2080TI to a 4070 and they've all got laggy once the city is medium sized. FPS'es of 20 to 30. The one thing that I've seen make the biggest difference is going from 32gb to 64gb.