If you don’t know react, skip it.
An extension can just be pure HTML/JS/CSS. No need to faff about with React.
Without seeing your code, I can’t comment as to why twitch.ext.onAuthorized is not firing, usually this might be due to other Javascript errors that should be provided via the console.
Helper actions (follow)
Doesn’t mentioned if a user needs to share their ID first, but it probably doesn’t (have not tested).