Getting "TypeError: Router.use() requires a middleware function but got a Object at Function" for this challenge

You seem to have removed the export from the bottom of the file.

var express = require('express');
var app = express();

app.get("/", (req, res) => {
  res.send("Hello Express");
});

module.exports = app;

I’ve edited your post for readability. When you enter a code block into a forum post, please precede it with a separate line of three backticks and follow it with a separate line of three backticks to make it easier to read.

You can also use the “preformatted text” tool in the editor (</>) to add backticks around text.

See this post to find the backtick on your keyboard.
Note: Backticks (`) are not single quotes (’).