Mongoose error when deploying on Heroku nodejs

I have completed a project and trying to deploy on heroku. I am using Reactjs frontend and express Nodejs with mongoose and mongodb in the Backend. It works on localhost but when I run Build it and try to deploy it on heroku it gives an application error.

Here is my backend connection code:

require('dotenv').config();
const express = require('express')
const session = require("express-session")
const bodyParser = require('body-parser')
const cors = require('cors')
const zomatoRoutes = require('./Routes/zomato')
const paymentRoutes = require('./Routes/payments')
const mongoose = require('mongoose')
const passport = require("passport")
const MongoStore = require('connect-mongo');


const uri = process.env.MONGO_URI || 'mongodb://localhost/zomato';

console.log(uri,'this is the mongo Atlas uri if connected using that !!!')

const options = {
    useNewUrlParser: true,
    useUnifiedTopology: true,
    dbName:'zomato1'
}

const connectDB = async () => {

    await mongoose.connect(uri, options ).then(() => {
        console.log('mongo connected')
    }).catch( e => console.log(e))
}


connectDB().then(() => {
    
    app.listen( process.env.PORT ||5252 , () => {
        console.log("express app is up and running on port 5252");
    })
})

I also have mongo session store the mongoose session when user logs in

app.use(session({
    secret: "this is unambigous secret",
    resave: false,
    saveUninitialized: false,
    cookie: { maxAge: 24*60*60*1000 },
    store   : MongoStore.create({ 
        client: mongoose.connection.getClient(),
        dbName:'zomato1',
        ttl: 14 * 24 * 60 * 60
     })
    
}));

app.use(passport.initialize());
app.use(passport.session());

It gives me MongoNotConnectedError: MongoClient must be connected to perform this operation error when I try to deploy using

git push heroku master:main

full error tail :

mongodb+srv://vishal_torne_22:********@db-first-hernode.zu6btrs.mongodb.net/<DBNamecomeshere>?retryWrites=true&w=majority this is the mongo Atlas uri if connected using that !!!
2022-07-31T11:19:34.581869+00:00 app[web.1]: /app/node_modules/mongodb/lib/utils.js:367
2022-07-31T11:19:34.581876+00:00 app[web.1]: throw new error_1.MongoNotConnectedError('MongoClient must be connected to perform this operation');
2022-07-31T11:19:34.581877+00:00 app[web.1]: ^
2022-07-31T11:19:34.581877+00:00 app[web.1]:
2022-07-31T11:19:34.581878+00:00 app[web.1]: MongoNotConnectedError: MongoClient must be connected to perform this operation
2022-07-31T11:19:34.581878+00:00 app[web.1]: at getTopology (/app/node_modules/mongodb/lib/utils.js:367:11)
2022-07-31T11:19:34.581881+00:00 app[web.1]: at Collection.createIndex (/app/node_modules/mongodb/lib/collection.js:258:82)
2022-07-31T11:19:34.581881+00:00 app[web.1]: at MongoStore.setAutoRemove (/app/node_modules/connect-mongo/build/main/lib/MongoStore.js:147:35)
2022-07-31T11:19:34.581881+00:00 app[web.1]: at /app/node_modules/connect-mongo/build/main/lib/MongoStore.js:128:24
2022-07-31T11:19:34.581882+00:00 app[web.1]: at processTicksAndRejections (node:internal/process/task_queues:96:5)
2022-07-31T11:19:34.581882+00:00 app[web.1]:
2022-07-31T11:19:34.581882+00:00 app[web.1]: Node.js v17.9.1
2022-07-31T11:19:34.703486+00:00 heroku[web.1]: Process exited with status 1
2022-07-31T11:19:34.791551+00:00 heroku[web.1]: State changed from starting to crashed

I am using Mongoose to connect the Mongodb, It works on localhost without heroku but when I deploy it using heroku, It asks me to use MongoClient. Is it a requirement to use mongoClient on Heroku 20 stack, I also get warning to upgrade to new Heroku version, I tried to upgrade heroku using npm upgrade heroku to the specifed version it shows successful but again rolls back to heroku 20 stack.

here's what I tried but researching the previous answers :

1. I added on my mongodb atlas the whitelist 0.0.0.0/0 (includes you current IP address)
2. I tried to make the mongoose code async so that it connect firsts the database then app listens to the port.
3. changed the engine version so that it supports latest node and npm version on Heroku like:

{
"version": "1.0.0",
  "engines": {
    "node": "17.x",
    "npm":"8.x"
  }
}

Is it a requirement to use MongoClient on heroku 20 stack ? as the Error shows... and why it is showing error on Mongoose.connect()

Thanks in advance..!