Below are listed over 100 commentaries on Genesis that are free online, in various formats and platforms. All of them were published before 1920 but are preserved, mostly through large-scale repositories like Internet Archive, HathiTrust, Early English Books Online, and Google Books, in addition to Sefaria.
I've numbered them in loose order based on my recommendation of them; I've commented on those that I've consulted. This list was a bit of an experiment; in the future, I will try to order these by language and author.
This list is pretty extensive, but if you know Latin, German, or French, you can find even more over at PRDL.