Finasteride (Propecia)
Elon Musk has likely been using Finasteride (Propecia) to keep the rest of his native hair from falling out fast over the course of his 30´s and 40´s (for the last 15-20 years).
FUT Hair Transplant
Elon Musk got most of his hair transferred from the donor area onto the recipient area via FUT.
Elon has likely undergone 1 larger (4000-4500 grafts) or 2 medium-sized FUT procedures (2000-2500 grafts and 2000-2500 grafts).
FUE Hair Transplant
Elon has probably had also one FUE procedure with relatively small graft yield as his donor area doesn´t show any signs of FUE over-harvesting or donor area depletion with FUE. His donor area above and below the FUT scar shows very good hair coverage and density.
Scalp Micropigmentation
On some photos, Elon´s FUT scar is less visible than on others. It suggests, that he might have made use of scalp micropigmentation to have the surface of his scarred skin covered with pigment (especially on the left and right side, where the hair is naturally thinner and has lower density compared to the hair on the occipital region).