It seems counter intuitive, but most of the best books on blackjack were written years ago. Edward Thorp’s Beat the Dealer: A Winning Strategy for the Game of Twenty-One is the book that got me on my way.  It’s outdated now but is still a must-read.  Peter Griffin’s The Theory of Blackjack: The Compleat Card Counter’s Guide to the Casino Game of 21 deep dives into the mathematics of blackjack and is well worth the read.
Other great blackjack books that I highly recommend include books by Ian Andersen, Julian Braun, Bryce Carlson, Richard Canfield, Carlson Chambliss, Michael Dalton, Steve Forte, James Grosjean, Lance Humble, Mason Malmuth, Ken Uston, Lawrence Revere, Donald Schlesinger, Michael Shackleford, Arnold Snyder, Ralph Stricker, Stanford Wong, and Bill Zender.  This isn’t a complete list of course, there are other excellent books on the subject.