That’s a fair point and n8n should definitely cover this. What the example workflow from your article does is manually running the requests required for the client_credentials OAuth2 flow.
If you copy the JSON from the article straight into your n8n canvas you should see the actual nodes:
The article suggests entering your client ID as the basic auth username and your client secret as the basic auth password on the first node (and of course replacing the URL because you don’t want to send these to Twitter). Could you give that a go?