All I did was update the two mini’s I own in the home app with Beta update still switched on for it to get the RC audioOS
Once it completed I thought I’d give it a try and see if the feature was implemented yet so said hey siri what’s the temperature in my kitchen. It then said sorry this feature is still being setup. Please try again in a few minutes.
I tried again about 5 minutes later and it spoke the room temperature including a decimal point value which was 12.4 degrees Celsius.
After that this is when it showed up in home. Here’s the actual new icon that appears to view the temperatures.