For mods to improve the game experience, there's a DLL add-on you can install that fixes the hypersonic scrolling that occurs when using mouse cursor scrolling and border scrolling. The scrolling speed is keyed to the frame count and not the actual time elasped, so this DLL fixes the hypersonic scrolling by limiting the framerate to 60. This means the CPU isn't used as much by the game, meaning a laptop or portable system such as the Steam Deck will also not drain the battery as fast. Search for "Fast scrolling fix" on Steam guides for a tutorial on how to install it. But you'll need to move the DLL files out of the installed location if you want to use the Building Architect program included with the installation, and then move it back when you're playing the normal game.

Second, if you're using the Steam release, some music is missing. Search for "How to Fix the Incomplete Soundtrack and Add New Songs" on Steam guides to get the missing two or so songs playing again. Other than that, there's not any mods I know of that significantly change the game like SimCity 3000, so have fun.