Most elements lighter than iron are forged in the cores of stars. A star's white-hot center fuels the fusion of protons, squeezing them together to build progressively heavier elements. But beyond iron, scientists have puzzled over what could give rise to gold, platinum, and the rest of the universe's heavy elements, whose formation requires more energy than a star can muster.
source https://phys.org/news/2021-10-neutron-star-collisions-goldmine-heavy.html