Updated version of this post
My HomePod mini is now on version 16.4, so the the temperature and humidity sensors are enabled. The data properly shows up in the Home app on my various devices.
In my HomeKit iPad app running on Mac Catalyst, however, the data does not show up. I would expect the HomePod mini to show up in HMHome.accessories with a service of type HMServiceTypeTempatureSensor. I see all of my other HomeKit accessories, just not the HomePod mini.
I have tried with the latest Xcode (14.3) and highest available iOS Target and Minimum Deployment (16.4), macOS version 13.3. I have not, as of this writing, upgraded my HomeKit architecture, however.
Note that I haven't tried the app on an actual iPad (and the iOS simulator doesn't expose my HomeKit environment.)