Haven't found any relasenote anywhere yet.
Only difference I have seen which I really like, is that notifications with images now show that image on the watch. So someone sends you a sticker on whatsapp, or the ring doorbell spots someone at the front door, it shows that. Will need to test it with more images to see what exactly it shows.
I remember many years ago Ray Maker commenting about these exact updates as merely being what they say, i.e. 'supporting fabrication' of a slightly altered hardware version of the watch. For example, if a supplier of some small chip (like a voltage regulator or logic chip) has ended an older version, or there is a change of supplier, and the new chip needs a different 'setup' or 'reset' procedure, then all future watch firmwares will need to handle both hardware versions.
The above was a simplified explanation I concocted from memory of Ray's comment and my own limited knowledge of low-level hardware programming, but I believe it touches reality...