There is this one page listed below that talks about this, but I’m still new to PHP. I agree it should be easier to make an RSS feed from categories.
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It’s already built-in.
For instance, have a look at the options for wp_list_categories (function that many/most themes use to list categories). Not only can you turn on feed links, you can specify a feed image as well.
Experiment: If you’re using non-default permalinks, go to a category page and add /feed to the end of the URL.
If you use “pretty” permalinks, just add feed/
on the end of the url:
//myblog.com/wordpress/category/mycategory/feed/
will generate a feed for all posts in “mycategory”