How to count and keep how many uploads has been done on STM32F103C8T6´s flash memory ?

You could journal a sequence number over an available sector, and perhaps also keep track in an unused vector table entry on the app as it is written/updated each time.

Yes. I already have in my app a counter for write cicles done under app. But since the app can be uploaded many many times, I want to have a more accurated flash life expectation... That is why I thought in increment (and keep) the counter in the bootloader too...