Something many (me included) did not originally realise, was that the temperature sensor on the Galaxy Watch was not intended to display "body temperature". Firstly for the reason that it is only skin temperature (not body core temperature) and secondly that it was really intended to help compliment identifying sleep cycles etc.
So now the feature will be used, in partnership with Natural Cycles, in order to provide the most accurate menstrual tracking possible. There is also a setting on Health Connection to define what gets synced or shared to other apps, so it is possible to disable that and keep the data local (for the USA obviously due to legal issues there).
See Samsung Galaxy Watch 5 and Galaxy Watch 5 Pro will gain temperature-based cycle tracking
The feature will come in partnership with Natural Cycles in order to provide the most accurate tracking possible.