Stable Rust 2022 will include all of Stable Rust 2021, just with some more bug fixes, performance improvements and features. If anything from Rust 2021 becomes outdated then that happens because new features or syntax allow a much better way to do the same thing, not because the old thing no longer works.

That happens to most actively used languages. C# has seen some major evolutions in recent years and is 22 years old now, Java is 26 years old and has some major changes compared to what it was 7 years ago, and you can no longer discuss C++ (37 years old) without mentioning C++11 along the way.