According to a blog post, the update affects Xbox One Controllers that have Bluetooth support, the Xbox Elite Wireless Controller Series 2, and Xbox Adaptive Controllers.
Jakub Sisulak / Unsplash
The main new feature is Dynamic Latency Input (DLI) which will deliver controller inputs more efficiently to make gameplay more responsive. This is a feature that was exclusive to the Xbox Series X and is now making its way to the older controllers.