passport.js req.user is undefined in every route expect for one

I am very new to backend so forgive me if this sounds really basic but I am trying to use passport-google-oauth20 to let users log in through Google and then pass the user information to the ‘/’ route.

This is the part of my passport.js file:

passport.use(
  new GoogleStrategy(
    {
      clientID: process.env.CLIENT_ID!,
      clientSecret: process.env.CLIENT_SECRET!,
      callbackURL: process.env.CALLBACK_URL,
    },
    async (accessToken, refreshToken, profile, done) => {
      // Get the user data from Google
      const newUser = {
        googleId: profile.id,
        displayName: profile.displayName,
      };

      try {
        // Check if the user exists in the database
        let user = await User.findOne({ googleId: profile.id });
        if (user) {
          done(null, user);
        } else {
          // Add the user to the database
          user = await User.create(newUser);
          done(null, user);
        }
      } catch (err) {
        console.error(err);
      }
    },
  ),
);

passport.serializeUser(function (user, done) {
  done(null, user);
});

passport.deserializeUser(async function (id, done) {
  const user = await User.findById(id);
  done(null, user);
});

Deserializing works great cause I checked and it returns the user info, but when the user gets redirected after a successful callback I can’t access req.user in any of the routes.
Those are my routes:

// Google auth
authRouter.get(
  '/auth/google',
  passport.authenticate('google', { scope: ['profile'] }),
);

authRouter.get(
  '/auth/google/callback',
  passport.authenticate('google', {
    failureRedirect: process.env.CLIENT_URL }),
  (req: Request, res: Response) => {
    // Successful authentication, redirect home
    res.redirect(process.env.CLIENT_URL!);
  },
);

I made this just to see if req.user would work here but it is undefined.

authRouter.get('/', (req: Request, res: Response) => {
  console.log(req.user); 
});

I can’t access req.user anywhere outside of the ‘auth/google/callback’ route. What am I doing wrong?

const app = express();
app.use(
  cors({
    origin: process.env.CLIENT_URL,
    methods: 'GET,POST,PUT,DELETE',
    credentials: true,
  }),
);
app.use(express.json());
app.use(express.urlencoded({ extended: true }));
app.use(cookieParser());
app.use(
  session({
    secret: process.env.SECRET!,
    resave: false,
    saveUninitialized: true,
  }),
);
app.use(passport.initialize());
app.use(passport.session());

connectDB();
app.use(authRouter);

Please help, I’ve looked everywhere.