[Kerrick]

The PickAxe is still amazing. You can buy the fifth edition (for Ruby 3.3) in paper now, or the sixth edition (for Ruby 4.0) as a beta ebook now.

5th: https://pragprog.com/titles/ruby5/programming-ruby-3-3-5th-e...

6th: https://pragprog.com/titles/ruby6/programming-ruby-4-6th-edi...

For a timeline-oriented reference of changes, check out https://rubyreferences.github.io/rubychanges/ and its individual pages.