Most of the feeds I subscribe to came to me in one of two ways:

1. I enjoyed reading an article posted somewhere else (Lemmy, etc.) so I sought out the feed of that publisher.
2. Sometimes news outlets enter into agreements to republish each others articles. When they do this, the re-publisher will usually include a little blurb at the end giving credit to the original publisher. If a feed I'm already subscribed to has an article re-published from elsewhere then I click through and check out the original source to see if I want to follow them as well.

Kagi Small Web, personally. Also a lot of people who blog on the Fediverse have RSS feeds, so discovery via Mastodon and such is good too.

Wordpress sites publish an rss feed by default at site.com/rss or site.com/feed, so there's a good chance a site you want an rss feed for has one even if they didn't intend to.

My way is simple and stupid. I hit F12, then search for “rss” in the html and copy the link

• Look around in your online communities and see what publications get shared.
• Once you find some sites you like, search the web/communities for alternatives with the same topic/vibe.
• If you find journalists you like, see where else they publish their works, or what publications they used to work at. For bloggers / content creators, see who they collaborate with.

I use an extension that searches the code on the page to find them. It puts a little number up, then when you click it you can copy the link.

You can set Google alerts for search terms. You'll get articles when they pop up. Apparently I have the same name as a politician in Canada, so I get to keep up with what's going on with that.