Mesa 23.3.1 brings a number of RADV bug fixes, various Intel ANV Vulkan fixes, a few Direct3D 12 driver fixes from Microsoft, a DriConfig workaround for Hades with Vulkan, and other small random fixes throughout. There isn't anything too particularly exciting with Mesa 23.3 being in rather good shape.
The list of Mesa 23.3.1 fixes can be found via the release announcement for those interested.
With Mesa 23.3.1 now being out, this effectively puts an end to the poorly managed Mesa 23.2 release. Mesa 23.2 never ended up seeing any point releases or updates in three months, so those wanting the best open-source OpenGL and Vulkan driver support on Linux are best off moving to the Mesa 23.3 series if you haven't done so already or aren't one riding Mesa Git.