Call of Duty: Modern Warfare II does support crossplay on PlayStation 4, PS5, Xbox One, Xbox Series X, and PC (via Steam and Battle). This means regardless of your platform, you'll be able to play with users on other systems or devices.

Call of Duty: Modern Warfare 3 can be played on PlayStation 5, PlayStation 4, Xbox Series S|X, Xbox One, and PC.

Cons of using an app\n\n If you use an app on your smartphone for authentication and the battery goes dead or the device breaks or gets stolen, you could get locked out of your accounts. Ensuring that you have the app set up on multiple devices like a smartphone and a tablet can help reduce your risk of being locked out.

Without access to the old authenticator, there's no way to recover the codes from it. You'll have to do account recovery on each of the configured account to regain access so you can configure them again. Without access to the old authenticator, there's no way to recover the codes from it.