I haven’t used RSS in a long long while but one problem I had with it was filtering. This was especially true where a site had frequent updates, say a news site, but there was no way to filter on the feed by topic unless the site provided custom feeds for each topic/category/tag. Has this gotten better?
From skimming around it looks like this still might be a limitation.
https://aktu.io is a news aggregator / rss reader that does just that. It automatically categorizes your feed items (politics, science, tech, etc...), extract topics and aggregates your feed items to news stories. You can then browse/filter your feeds by categories/topics.
NewsBlur has a filtering feature, but I don't see a way to tweak it beyond mashing thumbs-up and thumbs-down buttons and hoping it gets the idea. Might be worth a shot, though, it's definitely better than nothing.
If the feed contains tags, you can do this per tag. But sadly there's nothing inferred / you can't do it based on other content. There are definitely some feeds I follow where I'd immediately filter out an author or three, but alas.
From skimming around it looks like this still might be a limitation.