npx and create-react-app make it easy to create a new app running React and TypeScript.
npx create-react-app my-app --template typescript
Then you go into the folder and run the app.
cd my-app
npm start
You can create a JavaScript (non-TypeScript) app by removing the last bit—--template typescript. And you can also run the app with yarn start.
If, as I was, you're not getting the app working, you might have an older global installation of create-react-app. In my case I installed it with npm install -g create-react-app (which I could verify by running create-react-app -V on the Terminal. To make sure npx uses the latest version of create-react-app you need to uninstall the global version installed with npm.
npm uninstall -g create-react-app
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