How to create an entry in the mongdb database?

Question

MongoDB

Hello, I'm writing a REST API, but I can't seem to write a function to create a

Server.js entry:

// server.js
const express       = require("express");
const MongoClient   = require("mongodb").MongoClient;
const bodyParser    = require("body-parser");
const colors        = require("colors");
const db            = require("./config/db");
const app           = express();
const port          = 8000;

app.use(bodyParser.urlencoded({ extended: true }));

MongoClient.connect(db.url, { useUnifiedTopology: true }, (err, database) => {
    if (err) return console.log(err);

    const maindb = database.db("maindb")
    maindb.collection("posts")

    console.log("server has been connected to database!".green)
    
    require("./app/routes/index.js")(app, {});

    app.listen(port, () => {
        console.log("Server has been started on port... ".green + port);
    });
});

index.js:

const postRoutes = require("./post-routes.js");
module.exports = function(app, db, posts_collection) {
    postRoutes(app, db, posts_collection);
    // route handlers will be here...
};

post-routes.js:

module.exports = function(app, db, posts_collection){
    app.post("/post", (req, res, posts_collection) => {
        const post = { text: req.body.body, title: req.body.title };
        
        posts_collection.create(post, function(err, res) {
            if(err) {
                return console.log(err)
            }
            console.log(result.ops)
            client.close()
        })

        console.log(posts_collection)
        res.send(post)
    });
};

db.js:

module.exports = {
    url : "хотел украсть? а не!)"
}

when running and sending a post request through Postman, it gives the following:

server has been connected to database!
Server has been started on port... 8000
TypeError: posts_collection.create is not a function
    at E:\code\js\REST_API\app\routes\post-routes.js:5:26
    at Layer.handle [as handle_request] (E:\code\js\REST_API\node_modules\express\lib\router\layer.js:95:5)
    at next (E:\code\js\REST_API\node_modules\express\lib\router\route.js:137:13)
    at Route.dispatch (E:\code\js\REST_API\node_modules\express\lib\router\route.js:112:3)
    at Layer.handle [as handle_request] (E:\code\js\REST_API\node_modules\express\lib\router\layer.js:95:5)
    at E:\code\js\REST_API\node_modules\express\lib\router\index.js:281:22
    at Function.process_params (E:\code\js\REST_API\node_modules\express\lib\router\index.js:335:12)
    at next (E:\code\js\REST_API\node_modules\express\lib\router\index.js:275:10)
    at E:\code\js\REST_API\node_modules\body-parser\lib\read.js:130:5
    at invokeCallback (E:\code\js\REST_API\node_modules\raw-body\index.js:224:16)

How to normally implement the creation of records?