I had the same problem and found a workaround. Though I am on Windows 10, so I can't be 100% sure it will work for 11, but probably it will.
Go to your whatsapp folder in users/(your user name)/appdata/local (make sure you have hidden folders visible). You'll see two folders, app-2.2134.10 and app-2.2138.13, both have their own whatsapp.exe that will open the app. You'll notice however that the newer folder for version .13 does not have the file ffmpeg.dll, but the older version's folder does. That is why the updated .exe won't open.
For now you can use that launcher in the older folder. I didn't want to reinstall because I wasn't sure if I had backed up my old chats.
Please let me know if you have reinstalled and if that fixed the issue.
