It’s rubbish.
I wear my watch on the inside of my wrist, always have done. I’d noticed that the reported temp was always around 30’ C which I thought was odd. I then noticed while out on a run that in holding my arms the way I did I was effectively sandwiching my watch between my wrist and my chest. Aha, cause discovered. So I’ve done two or three runs with my watch on the outside of my wrist (it feels very odd) and the temperatures it’s now reporting are lower. It still takes it a long time to fall while,I’m out on a run, and I believe it’s still reading high. Like I say, rubbish.
It’s just as well it’s not an important metric 🤓