Image 5 from Atropos: Primordial Nucleosynthesis versus Stellar Nucleosynthesis is very enlightening, but it completely omits the enormous distinction that Big Bang nucleosynthesis has free neutrons (as discussed above) and stellar nucleosynthesis does NOT.

Another difference of Big Bang nucleosynthesis from stellar nucleosynthesis (omitted in Image 5) is that heat energy feedback from the nuclear reactions in Big Bang nucleosynthesis is NOT important in Big Bang nucleosynthesis. The universal expansion of the cosmic photon gas (AKA cosmic background radiation) controls the cosmic background radiation temperature.

In stellar nucleosynthesis, the heat energy from nuclear burning is a key ingredient in setting temperature.