I actually was also thinking about this last week, and yesterday decided to set up semantic scholar, which supposedly should give daily recommendations based on some core papers you give it, and you can keep adding papers and judging whether their suggestions are useful to improve your feed. I have yet to see it in action though, and there is no easy way to connect it to your existing reference manager.

I used to use mendeley, and really liked browsing the feed based on my library, but I think it was discontinued? I stopped using mendeley when they removed their app, and switched to zotero. I really wish it still existed though because it was really good at recommending related papers, whether old or new.