Query feeds by category for separate links?

This ones got me stumped, so I have a personal todo list:
https://todo.bradyjfrey.com/

That I’ve built under wordpress. I’ve customized it heavily so that categories of the specific list go under the specific column (as well as much more). Anything that is marked as completed goes into the side column and then has a single page link with the full outline of the accomplished task. So by customizing the template, only the completed tasks have an individual direct url.

I’d like the same thing to happen to my feeds, and that I can’t figure out in the files.

In short, I’d like, say, everything from Category 3 to query the full permalink_single_rss in it’s feed. Yet the other 1 and 2 categories to simply get bloginfo_rss(‘url’) in their feeds. It doesn’t make much sense to me how I could do that with PHP – any way to query specific categories get a different feed tag for links? thank you:)