Hello Parker Shaw,
I'm sorry you're dealing with this. That prompt to "send a code to an email you don't know" usually means the hacker changed the security info on your Microsoft account, so the verification code now goes only to their address, not yours. The launcher isn't really the problem here. It's just following whatever email is attached to the account.
The tricky part is that switching that email is the one thing that can't be done manually. You'd need to be signed in to change it, but signing in needs the code that's currently going to the hacker.
- Can you still sign in to your Microsoft account anywhere, for example in a browser at https://account.microsoft.com or on a PC where you're already signed in? If yes, you may be able to remove the unknown email yourself, which is a faster route.
- If you can't, the only path is the Microsoft account recovery form at https://account.live.com/acsr. If the first attempt doesn't work, try again from a different device or network, ideally in an InPrivate/Incognito window, and check your inbox, junk, and spam.
If the recovery form doesn't succeed after a few tries, then unfortunately, there isn't another supported way to regain access once the security info has been changed.