Google deprecated the old RSS feed URL format December 1st 2017 (deprecation notice), in addition to that they dropped the button in the Google News interface to generate a RSS URL (news mentioning this change).
This means that there is no public or documented method of generating a new RSS link. The only documentation they have is out of date since they changed the interface.
What is the new format for generating a RSS feed for a Google News topic?
Found an up-to-date library (1) that uses Google News RSS.
The URL new format seems to be:
Top news:
https://news.google.com/news/rss
By major topic:
https://news.google.com/news/rss/headlines/section/topic/{topic}
Where {topic} is one of the following values: WORLD NATION BUSINESS TECHNOLOGY ENTERTAINMENT SPORTS SCIENCE HEALTH
By any/custom topic:
Once at https://news.google.com, browse to the desired topic, for example this. Identify the topic ID in its URL, e.g. CAAqIQgKIhtDQkFTRGdvSUwyMHZNR056T1hFU0FtVnVLQUFQAQ, and use the format:
https://news.google.com/rss/topics/{id}?hl={lang}
In the format above, essentially rss/ is added after https://news.google.com/.
By geolocation:
https://news.google.com/news/rss/headlines/section/geo/{location}
Not sure about the formatting for the {location} parameter
By search query:
New link: https://news.google.com/rss/search?q={query}
Old link: https://news.google.com/news/rss/search/section/q/{query}
Where the {query} parameter is a free text search
Specifying country and language:
For example if you wish to have news in Swedish and located from Swedish sources, add the following query string to the URL to change country and language to sv-SE:
?hl=sv&gl=SE&ceid=SE%3Asv