Okay, contrary to what I previously thought, further research shows that extended: true and app.use(bodyParser.json()) can be used together. So it is not only extended: false that uses it. The statement app.use(bodyParser.json()) is to be used independently, whether you set extended as true or false.
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app.use(bodyParser.json())basically tells the system that you want json to be used. -
bodyParser.urlencoded({extended: ...})basically tells the system whether you want to use a simple algorithm for shallow parsing (i.e. false) or complex algorithm for deep parsing that can deal with nested objects (i.e. true).
Have a look at the docs (i.e. https://expressjs.com/en/guide/migrating-4.html) for the example.