It's in the megathread linked in this comment, but I want to specifically point to https://open-slum.org/ which is basically a status page for different sites dedicated to this purpose, and which I've found helpful.
Lol. I opened that link and was like "hmmm, that UI looks familiar".
Life pro tip: the Wikipedia pages for Libgen and Scihub contain up-to-date current links in the right sidebar. Only for the purpose of information and documentation, of course.
I believe that there's a reddit sub that keeps people up to date with what URLs are, or are not, functioning at any given point in time