The Home app shows less precise temperature compared to temperature in Widgets or when asked Siri

I experience the same. I have Eve Weather in every room in my house, and two motion sensors from Hue - which can also measure the temperature. Both Eve and Hue only show ex 21.0 or 21.5 in Apple's Home app.

If I look in Eve's own app, I get the exact temperatures. The Hue app does not show temperatures on their sensors. I also get the exact temperature when I ask Siri. But for sure it's a HomeKit thing - it's been like that all the time I've used the Eve Weather Stations, which is a few years now.

So you are not the only one experiencing it. My advice is that if you want the exact temperature, use the app that your smart devices come with - maybe try to make a widget via that app.

You're welcome.

No, you can't do anything different, that's how it is at the moment. However, I thought it was because I had 3rd party devices that it didn't give the exact temperature, so that HomePods don't give accurate temperature either surprises me. But then I also learned something new today, thanks.