Debian Bookworm itself is mostly made up of incremental updates of the software that was in the previous Debian Bullseye release. There are a few small changes — have a look here for the list — but they mostly won’t affect Raspberry Pi users. So Bookworm itself really hasn’t resulted in many changes.
However, for the last year or so we have been working on some major architectural changes to the Raspberry Pi Desktop, and these are launched for the first time in the Bookworm release. And this is where you might notice some differences.
With this new release, Raspberry Pi OS moves to Wayland and a Wayfire desktop, but it looks and feels exactly the same as what came before with X.Org. It now also comes with Pipewire, as well as an up-to-date version of Firefox that has been modified in cooperation with Mozilla to make better use of the hardware features found in the Pi.