How to write type definitions for firebase objects in react?

I am trying to integrate firebase with react-native(expo). I followed the firebase documentation found here. The documentation was quite straight-forward and works as intended, but since the document is in JS and I am coding in typescript, I am receiving quite a few errors on my linter.

So few points about the code below

1. i have defined the SuccessfullyAuthenticatedUser because the type of parameter changes when I call the method onSignIn(result) within signInWithGooglAsync
2. in onSignIn function i am recieving a value from firebase. The value received comes with type definitions, but value.additionalUserInfo.profile is defined as Object | null | undefined, therefore i am unable to access the values inside profile Object without explicitly defining profile as any. ESlint is kinda mad at that.
3. In the isUserEqual function googleUser object has no method called getUserProfile().getUserId(). I tried to explicitly define type for that but I do not know how to define types for functions(classes?) which have functions of their own

I am quite sure that I am doing a lot of things wrong, and chasing down a rabbit hole. So someone please suggest me how to implement this in a better way or tell me how I resolve point 2 and 3.

interface SuccessfullyAuthenticatedUser {
  ...
  type: "success";
  getBasicProfile?: any;
}

const signInWithGoogleAsync = async () => {
    try {
      const result = await Google.logInAsync({...});

      if (result.type === "success") {
        onSignIn(result); 
        ...
      }
      ...
    } catch (e) {
      ...
    }
  };


const onSignIn = (googleUser: SuccessfullyAuthenticatedUser) => {
    ....
    ....
        firebase.auth().signInWithCredential(credential).then((value) => {
            const profile: any = value.additionalUserInfo?.profile;
            firebase.database().ref(...).set({
              ...
              first_name: profile.given_name,
            });
          })
      ...
  });
};

const isUserEqual = (
    googleUser: SuccessfullyAuthenticatedUser,
    firebaseUser: firebase.User | null,
  ) => {
    if (firebaseUser) {
      if (providerData[i]!.uid === googleUser.getBasicProfile().getId()){
            ...
      }
    return false;
  };