Your performance Guide and PSA for C:S II https://www.reddit.com/r/CitiesSkylines/comments/17efe6b/your_performance_guide_and_psa_for_cs_ii/
Start with a High Preset and then
Use "Fullscreen Windowed" or disable VSync
Disable "Depth of Field Mode"
Reduce "Volumetrics Quality" to Low
Disable "Global Illumination"
Reduce the "Level of Detail" to Low (or Medium if you don't need the extra FPS)
Disable "Motion Blur" (This is a preference, if you want it, keep it on Low)
In the advanced tab, scroll to the Shadows section and disable "Terrain Casts Shadows"
If you want to squeeze a bit more performance, Disable "Fog Quality", though I personally prefer to keep it enabled
Tips: Our Guide to Optimize Performance https://forum.paradoxplaza.com/forum/threads/tips-our-guide-to-optimize-performance.1603423/
Lowering the Resolution; we recommend 1920 x 1080 x 60Hz
Disable Depth of Field
Disable Volumetrics; this lowers the quality of the volumetric clouds.
Motion Blur, Depth of Field, and Dynamic Resolution:
While these three will not always improve your performance, we wanted to help you understand what these settings are and hopefully help solve potential “why-does-my-game-look-like-this” questions.
Depth of Field and Motion Blur can cause the game to look very strange and motion sickness and can cause low FPS to feel worse.
Tilt Shift Depth of Field and Motion Blur can be very visually disruptive if you have low FPS.
Dynamic Resolution is a game setting that helps with performance by dynamically changing the resolution. Dynamic Resolution can save FPS but might make the game look blurry; here’s an example;
Turning it to “Automatic”.
Turning it to “Constant”.
These three settings are optional, and we encourage you to change the setting to find what suits you best.