This version includes the following non-breaking changes:
Other
* Fix for grpc.tools #17995 & protobuf #7474 (handle UTF-8 paths in argumentfile) (#10721)
C++
* 21.x No longer define no_threadlocal on OpenBSD (#10743)
Java
* Mark default instance as immutable first to avoid race during static initialization of default instances (#10771)
Ruby
* Auto capitalize enums name in Ruby (#10454) (#10763)
You can view the release on GitHub.
If you experience any issues with the release, please file a bug or post on the Protocol Buffers forum.