I maintain quite a few packages on Nixpkgs, so I use Atom to subscribe to a release feeds for those projects so I can get a form of notification independent of the project’s code forge (mostly meaning I can spend less time on MS GitHub).

I mostly use it for news, but a lot of sites have RSS even some that do not advertise it.

Whenever I like a site I usually use rss validator and check if their blog/news page have RSS.

Additionally I check endpoints like /rss and /feed.

Not the most concrete answer, but what you subscribe to is highly personal.

P.S. I also use something like https://ktnrs.com/ for websites providing only email newsletter.

Depends on what you are looking for. Some from the top of my head - only English sources:

• https://www.xkcd.com/
• https://www.smbc-comics.com/
• https://pluralistic.net/
• https://thedailywtf.com/
• https://buried-treasure.org/
• https://googleprojectzero.blogspot.com/
• https://parliamentfights.wordpress.com/
• https://research.checkpoint.com/
• https://isc.sans.edu/
• https://this.weekinsecurity.com/