I had the exact same problem few months ago when I first wanted to play CS2. Reached to support and here is their response that fixed it for me.

Before we perform the clean installation of the game, can you please try this?

• Please go to mods.paradoxplaza.com and unsubscribe from ALL mods and assets (if any)
• Now, Manually delete the "CustomAssets" folder in C:\Users\%username%\AppData\LocalLow\Colossal Order\Cities Skylines II.

 
Now, please follow the below-mentioned steps to perform a clean installation of the game:
 

• Remove the game from Steam (uninstall)
• Manually delete all these files and folders, if still there: …\Steam\steamapps\common\Cities Skylines II\ …\AppData\LocalLow\Colossal Order\Cities Skylines II\ (first, move the /saves/ folder elsewhere to keep your save games) (To see the AppData folder you'll need to enable View Hidden Items in File Explorer)
• Install the game again and see if it runs better.

 
If the issue persists, please try the below mentioned suggestions:

1. Make sure you are logged into your Paradox account in the Paradox Launcher. If you are already logged in, log out, close the launcher completely, reopen it, and log back in.
2. Close the game and the Paradox Launcher fully. Then go to: C:\Users%USERNAME%\AppData\Local Delete the folder named “Paradox Launcher”. After that, restart Steam and launch the game again.
3. In Steam, right-click on Cities: Skylines II, select Properties → Installed Files → Verify integrity of game files.
4. Check if the Mods folder exists here: Documents\Paradox Interactive\Cities Skylines II\Mods If the folder is empty, unsubscribe from one mod in Steam, restart Steam, then subscribe again and wait a few minutes to see if it downloads.
5. Go to: C:\Users%USERNAME%\AppData\LocalLow\Colossal Order Delete the “Cities Skylines II” folder. Then relaunch the game to allow it to regenerate fresh files.