agnos.is Forums

I'm not the person you replied to, but they say in their comment they use Get RSS Feed URL.

Here's a short blog post that summarizes how to use Full-Text RSS with FreshRSS. It's a bit of a pain to add new feeds but it makes for a smooth experience afterwards.

Otherwise, you could always just use RSS clients that have the ability to fetch full articles, Read You on Android and Fluent Reader on desktop both can do this.