A Max Shadow Distance slider is now available in Video Settings, allowing you to tweak the render distance of shadows on packs that don't specify one.
It no longer incorrectly culls chunks compared to OptiFine, and overall performance has improved greatly compared to the previous system (especially with shader packs like Enhanced Default, BSL, and Complementary Shaders).
Shadow culling has been completely rewritten.
For 1.17.1 and above, this release also contains a modified version of Sodium based on 0.3.2 instead of 0.3.0 like before, improving performance and graphics driver compatibility.
This release includes a new shadow culling system as well as a new batched entity rendering system, improving performance with many shader packs and fixing a bunch of bugs!.
A more detailed changelog is available on GitHub for those who are interested.