Express not importing with Typescript

I’m starting a new Node.js project with Typescript. This works fine:

server.ts

const express = require("express")
const app = express()

app.listen(3000, () => {
    console.log("Server running")
})

But this was before using Typescript, for this project I use this configuration:

import express from 'express'

const app = express()

app.listen(3000, () => {
    console.log("Server running")
})

But the app crashes, it gives the error message:

SyntaxError: Cannot use import statement outside a module

In tsconfig.json, I just changed the lines:

"target": "es2021",
..................
"outDir": "./build",

The package.json scripts:

"scripts": {
    "dev": "node --env-file=.env --watch server.ts",
    "build": "tsc",
    "start": "node build/server.js"
  },

So what could be the problem?