Google Discover is not a fast-track way to get onto Google News. The only prerequisite to getting on Google Discover is that your pages are indexed by Google and meet all of the Google News requirements.
While that may sound like it’s a way to get into Google News, it’s not. Some articles have been accepted by Google Discover and denied by Google News.
It’s best to consider Google Discover as a step toward getting closer to Google News, but the two are not interchangeable.