Session stored in database, but not in browser

I am a bit rusty with sessions and authentication so bear with me. I am attempting to make a simple login function for my site, users can sign up successfully and their information gets stored within MongoDB. When trying to have a user login, and create a session ID, i can see the session get stored in my ‘sessions’ collection, but not within the ‘cookies’ on the browser, I also cannot access the “logged in” users data once they get past the login page.

Using mongoose, express-session, and connect-mongo

Users.js

router.post('/login', async (req, res, next) => {
    const { username, password } = req.body
    const user = User.findOne({ username: username })
        .then(async (response) => {
            if (!user) {
                return res.send('User not found')
            }
            bcrypt.compare(password, response.password, function (err, result) {
                if (result !== true) {
                    return res.status(500).json(err)
                }
                req.session.user = {
                    username,
                    password,
                    isLoggedIn: true
                }
                req.session.save()
                res.status(200).send()
            })
        })
        .catch((err) => {
            console.error(err)
            res.status(400).json({ error: 'Internal Error' })
            return
        })
})

server.js

mongoose.connect("mongodb://localhost/BookNest")

app.use(session({
    secret: 'my-secret',
    resave: false,
    saveUninitialized: true,
    store: MongoStore.create({
        mongoUrl: "mongodb://localhost/BookNest"
    })
}));

Ive attempted to console log req.session and req.sessionID both of which return my ‘session id’, but still cannot do account actions once logged in.