Some highlights since the last LTS (JDK 11):

  Language Features
  394: Pattern Matching for instanceof
  395: Records
  306: Restore Always-Strict Floating-Point Semantics
  409: Sealed Classes
  361: Switch Expressions
  378: Text Blocks

  Language Features in Preview (behind a flag)
  406: Pattern Matching for switch
  412: Foreign Function & Memory API
  414: Vector API

  Tooling
  392: Packaging Tool (jpackage)

  JVM
  386: Alpine Linux Port
  391: macOS/AArch64 Port
  340: One AArch64 Port, Not Two
  388: Windows/AArch64 Port

(Source: https://openjdk.java.net/projects/jdk/17/jeps-since-jdk-11)