Java21 is new java language in feature in progress and release phase

Java21 features list

430: String Templates (Preview) 431: Sequenced Collections 439: Generational ZGC 440: Record Patterns 441: Pattern Matching for switch 442: Foreign Function & Memory API (Third Preview) 443: Unnamed Patterns and Variables (Preview) 444: Virtual Threads 445: Unnamed Classes and Instance Main Methods (Preview) 446: Scoped Values (Preview) 448: Vector API (Sixth Incubator) 449: Deprecate the Windows 32-bit x86 Port for Removal 451: Prepare to Disallow the Dynamic Loading of Agents 452: Key Encapsulation Mechanism API 453: Structured Concurrency (Preview)

Reference

Java21 - Features