I came up with solution for overheating camera issue in Xperia phones.
Remove back panel of yiur phone
You will find metallic strip around camera sensor
You have to adjust this metaklic strip in such a way that it should ve in touch wid camera sensor from all sides(if all sides is not possible then get that metal strip as near as possible to camera)
That metal acts as heatsink for camera.
Sometimes it is not in touch with sensor.
Other option you can do us downloaf any other camera app from playstore
But it cant give high quality image capturing
However it wont show any temperature warning
PLEASE Hit Like button if you find my solution is working for you