Have you tried following these steps?
Disclaimer
If you're having framerate problems, try forcing the game to run on an NVIDIA graphics card, if you have one, or any other graphics card that has high OpenGL compatibility.
- Type "graphics settings" on the Windows search bar and open the top result (should say "system settings" right underneath it)
- Alternatively, open the settings app, then go to System > Display > Graphics
- Click "desktop app" and then "search"
- Find the .exe file for City Nightmare and double click it
- Click on "options" right underneath the file directory for City Nightmare
- Select your preferred GPU and click "save"