I built that feature (auto mark as read by scrolling) into my feed reader if you’re up to self host and curate your sources

https://github.com/facundoolano/feedi

I did try to build a public facing news aggregator with a similar ux but I couldn’t pull it off purely based on client side state (and I didn’t want to do user management)

I'm with you on not wanting to do user management, feature creep, user data security concerns, etc.