The only significant update I remember is when they switched to the new HomeKit architecture. That was with iOS 16.1 or something.
I don't think I upgraded to beta software on my HomePods for that, but I did manually update to the new architecture once it released, even though they pulled the ability to so so shortly after because it bricked many people's home setups (requiring it to be setup from scratch again). Worked fine for me and was better then ever in terms of responsiveness and reliability.