You can follow some simple steps shown below to fix both crashes.

1. Open the game and click on "Help and Options" in main menu.
   
   
2. Now click on "Video" and you will see your video settings.
   
   
3. Just change "Texture quality" to "Low" and click on "Accept". Now it shouldn't crash on loading.
   
   
   
   
4. If you still encounter the crash, then change the resolution to "1600x900" or lower.

You have to do the following steps each time you launch the game. It is required to do this on both Host and Clients.

1. Launch the game.
   
   
2. Now press CTRL+ALT+DELETE and click on "Task Manager" or you can press ALT+TAB to switch out of the game and open Task Manager by right-clicking empty area on your Taskbar on Windows 10. You have to right-click on Start menu icon on Windows 11 to open Task Manager.
   
   
   
   
3. Now go to "Details" tab in Task Manager and find "GodMode.exe". Right click on it, hover over "Set priority" option and click on "Realtime". It will ask for confirmation, just click "Change priority" button on confirmation window.
   
   
   
   
4. Now just switch back to the game by clicking on game icon from Task Bar or by pressing ALT+TAB to select the game. Now you can start your co-op session, and it should work without any issues.