Early in my career I benefited greatly from reading a few books on programming. There were two books in particular that I believe raised the level of what I was doing professionally. First was Steven Feuerstein's Oracle PL/SQL Programming (I think I had the second edition). The other came years later and was Head First Design Patterns by Freeman, Robson, Bates and Sierra.
So I know the benefit of reading programming books - especially when looking for a deep dive on a technology. Which is why I was happy a colleague sent me this link to an index of free programming books on GitHub. It covers a variety of languages and did I mention is free? The link is https://github.com/vhf/free-programming-books/blob/master/free-programming-books.md
No idea if the next book to help me level up as a professional is there, but I'm going to hope so.