It seems I've tried everything.
I just want an RSS reader that downloads things to different folders for every feed.

Welcome to LQ!
Thunderbird does RSS feeds.

Firefox does as well.

I use miniflux hosted on my own $35 Raspberry Pi 2.

KDE's Akregator works very nicely, but for one bit of clunkiness: If you are looking at a list of articles from a particular feed, you can't use CTRL-A to highlight all of them for deletion. You have to use CTRL-click or SHIFT-click to highlight threads.

There's an excellent Chrome plugin, which also works in Vivaldi, called "The RSS Aggregator."

The Seamonkey browser has an excellent built-in RSS aggregator.

I have not found an easy-to-use RSS plugin for Firefox, though I've been looking. The feature I've not been able to find in the Firefox plugins I've tried is the ability to import a feedlist in *.opml/*.html format. The ones I've tried seem oriented to adding feeds individually or selecting feeds from your bookmarks. (I don't necessarily bookmark the sites whose RSS feeds interest me. Bookmarks and RSS feeds are two different things. One thing is not like the other thing.)

Thanks, didn't realize this. Can you make it automatically download to a folder?

Using filters, that should be possible.

I can't figure out how to copy the items in the RSS feed (they look like attachments to an email) to my disk.
Also, can you save the password for the feed in Thunderbird? You can read the feed without authorization, but downloading the files requires a username and password.

How to Subscribe to News Feeds and Blogs
Organize Your Messages by Using Filters

From https://support.mozilla.org/en-US/products/thunderbird

Let us know where you get stuck. and possibly any rss feed(s) in question, after
you tried your luck with the first two links, or SeaMonkey, or Chrome+addon as suggested.

Have a Great Day!

How to Subscribe to News Feeds and Blogs
Organize Your Messages by Using Filters

From https://support.mozilla.org/en-US/products/thunderbird

Let us know where you get stuck. and possibly any rss feed(s) in question, after
you tried your luck with the first two links, or SeaMonkey, or Vivaldi and the Chrome+addon as suggested.

Have a Great Day!

Forum is on crack.

Which reader are you referring to?

The easiest way is generally to open the RSS link to the source in your browser and save it from the browser. If it's text, it may be easiest to copy the text to a text editor, then save the contents from there.

In the case of a podcast, depending on the reader, the feed might include a link to the media file. If it does, in the readers I've used, you can right-click on that link and click "Save/Save As" in the right-click dialog.

As an aside, I am not a fan of Thunderbird's feed reader. That's just me.