I use Miniflux as my feed reader. When I come across a site I want to subscribe to, I use Miniflux's bookmarklet first. Two recent sites (both built on WordPress) advertised problematic feeds to Miniflux. The first one had a messy feed in that it represented each part of multi-part series as an individual entry. The second had an empty site feed. Fortunately, both sites were easy to follow without any third-party tools. The solution: Look for the taxonomic feeds.

https://thenewleafjournal.com/finding-the-best-rss-atom-feed/