index.html at port 3000 isnt available after mongodb connection - mongodb

Question

im a bloody beginner in the node.js, mongo.db topic, i made some courses and now i want to combine those, but when i require my mongodb database, my index.html isnt available anymore on the localhost 3000:
when i comment those line out my localhost connection work:
app.use(require('./routes/posts'));
i think i made something in the inizialisation wrong, but im a bloody beginner, i have no idea what i did wrong.
my server.js:
const express= require('express')
const app= express();
const http= require('http').createServer(app)
const PORT=process.env.PORT || 3000
http.listen(PORT, ()=>{
console.log(`listening to port ${PORT}`)
})
app.use(express.static(__dirname + '/public'))
app.use(require('./routes/posts'));
app.get('/',(req,res)=>{
res.sendFile(__dirname + '/index.html')
})
//socket implementation
const io=require('socket.io')(http)
io.on('connection',(socket)=>{
console.log('connected')
socket.on('message', (msg)=>{
socket.broadcast.emit('message',msg)
})
})
routes/posts.js:
const express= require('express');
const router=express();
const Post=require('../model/post');
router.use(express.json);
router.post('/posts/new', (req,res)=>{
const post = new Post({
title:req.body.title,
content: req.body.content
})
post.save()
.then(result=> res.sendStatus(201))
.catch(err=>{
console.log(err);
res.status(500).json({error:err})
})
})
module.exports=router;
model/post.js:
const db= require('../database');
const postSchema= new db.Schema({
title: {type: String, require:true},
content: {type: String, require:true}
}, {timestamps:true});
const Post= db.model("Post", postSchema);
module.exports=Post;
database.js:
const mongoose= require('mongoose');
//const mongoose = require('mongoose/browser');
mongoose.connect('mongodb://localhost/accounts', ()=>{
console.log('mongodb connected');
})
module.exports=mongoose;
test.rest:
GET http://localhost:3000/
POST http://localhost:3000/posts/new
Content-Type: application/json
{
"title": "first",
"content": "test"
}
i want to achieve that i can use the post command in test.rest and it writes those into my local mongo db, while i can see on localhost 3000 the frontend.
thanks for help!