This fix uses a batch file to launch the game with the desired CPU affinity set. This has only been tested in Windows 11 w/ 7950X CPU.

1. Create a windows batch file with the following line in a text editor, like notepad. Change Launcher.exe with the Witcher's 2 launcher name with .exe at the end.
   
   • %comspec% /C start /normal /affinity 1ff Launcher.exe
     
     
   • 1ff is for 8 cores, f is for 4, please set accordingly to your hardware.
     
   
   
2. Save it, name it what you'd like, for this example I'll name it launchwaffinity.bat. Include .bat at the end of the name to create the batch file.
   
   
3. Place the batch file in the game's install folder.
   
   
4. Back in Steam, in the game's launch options type the following
   
   • <path-to-batch-file> %command%
     
     
   • i.e.
     "D:\SteamLibrary\steamapps\common\the witcher 2\launchwaffinity.bat" %command%
   
   
5. Click Play and (hopefully) enjoy!

Note 1: The path to the batch file in the launch options needs to be wrapped in double quotes ("example"). This is to escape the spaces and slashes, there are other ways but just do it like this ok.

Note 2: It's been mostly recommended to set the affinity to 4 but 8 cores work too, at least for me. Try it out.

Note 3: The equivalent can be done in linux, instead of a batch it'd be a script. As for %command%, I don't remember if it's the same in linux.

Note 4: I did not have to set a compatibility mode, nor set the launcher(s) to run as admin, nor anything else, just this.

This also works for other games that need their CPU affinity limited to run, like Assassin's Creed Director's Cut.