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.
Most of the feeds I subscribe to came to me in one of two ways:
I enjoyed reading an article posted somewhere else (Lemmy, etc.) so I sought out the feed of that publisher.
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.
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.