Use the luxury manufactory mechanic to improve late game district spam.

So one things that drives me nuts, and probably causes late game lag for slower systems is the district spams in the later eras, as the map fills up with countless districts. Here's a solution: impliment a system similar to civ 6 where you build on TOP of already existing districts to get higher yields.

Lemme explain: The luxury manufactory in the game already has the basic mechanic of this. Once u exploited a resource, eventually u can build "on top" of it to make it into a manufactory. Similarly, in the Industrial era, have the first techs unlock new district types that are like "heavy Industry/commercial/farmer/science District".

Essentially these districts are almost guaranteed to have a higher yield when build upon an already placed district and will thus cause the player and AI to tend to build more "tall" rather than "wide".

These district types MUST be build on pre-existing district types (commercial on commercial etc) and would help with simulating industrialization, urbanization, and generally lowering district spam late game. Since the mechanic kinda exists already, I feel like its a rather simple adjustment.

TL;DR: implement in the Industrial era & onwards a system similar to civ 6 where the player and AI are encouraged to build on top of current districts for higher yields instead of spamming more districts.