One of my favorite RSS readers is https://vore.website - river of news, no unread indicators, simple. It's a website, as the domain suggests, so no need to install anything.
Yeah, after the appropriate layers of VPN/Incognito/Tor/muted phone/etc I braved the link, and it turns out it's actually real, but that is still not a hostname I want connected to me in anyone's access logs more than once.
It's under the NON-VIOLENT PUBLIC LICENSE v5, which is probably not open source, but should be fine for personal use if you're not an arms dealer or prison warden.
There's more RSS readers than you can count. No need to pick a proprietary one with a sketchy license when there are tons of great open-source options.
It suggests a couple of things...