Disclaimer: not an expert in any of this, just stumbled across that page on Anna's Archive.

Sci-Hub is down (as in, you can't search/view/download papers from sci-hub.se), AFAIK.

Anna's Archive aggregates into a unified database material from Libgen.rs, Sci-Hub, Libgen.li, Z-Library, Internet Archive Controlled Digital Lending, and DuXiu 读秀. (See: https://annas-archive.org/datasets )