newsfeed discards feed items that use "a10:updated" tag instead of "pubdate" etc.
verify: https://www.tagblatt.de/Kreis%20T%C3%BCbingen.rss
[...]
const fetchNews = () => {
[...]
parser.on("item", (item) => {
[...]
const pubdate = item.pubdate || item.published || item.updated || item["dc:date"];
last line might be changed to
const pubdate = item.pubdate || item.published || item.updated || item["dc:date"] || item["a10:updated"];
Unfamiliar with PR, therefore included possible solution.
Thanks!