Iron is the heaviest element capable of being created inside stars, via fusion. Once iron is fused, the star begins to rapidly collapse.
Elements heavier than iron (28) are the result of supernova explosions, which produce energies high enough to create these heavier atoms. It is further possible, as described in the image, for very heavy elements to decay into lighter more stable elements, those still being heavier than iron.
That's what I learned in school, but there's been some research since suggesting stars produces significant quantities of elements up to lead during their lifetimes, even though it's a net energy loss.
Interesting. Of note, this process would mainly be in a very specific kind of star, and still would depend on an iron "seed" leftover from a previous supernova. Technically, still requires a "regular" supernova.
No. Nucleosynthesis of lead within stars generated from supernovae make up the bulk of the existing lead on Earth. Uranium decay does provide some additional lead inventory but would be fairly small in comparison.
But the presence of it in the first place within second generation stars proves that lead is billions of years old.