I think to connect to mongoose we might need to connect this way.

mongoose.connect(MONGO_URI).then(() => {
  console.log("connected to mongodb");
}).catch((e) => {
  console.log("could not connect to mongodb", e);
});

We would als need to install @types/cookie-session

And I think the logout function should be implemented this way

router.get("/logout", (req: Request, res: Response) => {
  req.logout(function(err) {
    if (err) {
      console.error('error when logging out', err);
    }
    res.redirect("/");
  });

});