I have the same error and the problem may be here:

import { GoogleAuthProvider } from '@angular/fire/auth';

.... (blah, blah, blah and lot of code here)
    signInWithPopup( this.auth, new GoogleAuthProvider() )
    .then( (userCred) => {
      console.log("this is the result of the promise" );
      console.log( userCred );
    })

the problem is the import statement. When I changed to:

import { GoogleAuthProvider, signInWithPopup } from 'firebase/auth';

The problem solved, at least in that part.