[2022] Game not completely closing

Hmm, that sounds very strange! The game can be a bit slow to shut down with a lot of workshop content, but not several hours! :S

Try adding the launch options -noWorkshop and -disableMods and see if it's the same with those in place.

How To Set Launch Options

• Right-click on the game title under the Library in Steam and select Properties.
  
• Under the General tab click the Set launch options... button.
  
• Enter the launch options you wish to apply (be sure to separate each code with a space) and click OK. Should look like this:
  -noWorkshop -disableMods
• Close the game's Properties window and launch the game.

Try doing a clean install of the game.

- Remove the game from Steam (uninstall)
- Manually delete all these files and folders, if still there:

...\Steam\steamapps\common\Cities_Skylines\
...\Steam\SteamApps\workshop\content\255710\
...\AppData\Local\Colossal Order\Cities_Skylines
(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)