This has been posted all over the place but if you haven’t seen it, this is a huge change.
To get it working, you need all your Apple TVs on iOS 18 DB1. Remove all your HomePods from your home if you have them. Then, you should see the option to turn off “Automatic Selection”. Turn it off and pick the Home Hub you want.
You can then readd your HomePods to your home. This process sounds painful but it’s actually pretty quick, HomePods remove, reset and readd to your Home fairly quickly. This whole process probably only took about 10 mins.
WARNING - After I did this, everything worked fine. However when I woke up the next day all the HomePods were showing “No Response”. Rebooting them and rebooting my Unifi UDR did nothing, they just refused to reconnect.
I was also messing around with Wifi to get some other older HomeKit devices to reconnect including deleting the saved WiFi network from my phone so they may have lost access because of that? However just a warning.
I was able to get them all readded but it required a full factory reset from the HomePods themselves because they couldn’t be controlled from the home app. Easy to do but annoying.