They need clones for bodies. Stem cells the best source of these is fetuses. Hence the Pfizer vaccine was made out of dead babies. Stem cells extend longevity and can give the brain longer life. But stem cells still haven't grown a brain, the brain hasn't been 3D printed, and haven't completely grown a body. You need a fresh body to put your brain into. While it is obvious they can clone humans and could possibly even speed up their ageing. It hasn't been reported due to public outrage. Despite increasing black ops and programs running in other parts of the World. Human cloning hasn't happened outside of artificial insemination where they have massively edited the DNA prior to birth, and also passed on bloodlines and eugenics.

But the brain ages. Dementia, Parkinson's, Bloodclots. It cannot live forever.

Perhaps there are vampires or aliens. Or even the fountain of youth. Or timetravel. Far better explanations. Otherwise it isn't possible. Outside of offering elites far better medical care often extending their lifespan to better ages than almost anybody else.

Despite it being documented that they can do brain transplants. The risk is at which percentage. Far too high. Nobody would take that risk unless they are terminal, or it had better odds of success. It doesn't at all.

Where the technology is at. Is at downloading your memory onto a computer, it storing your memory banks in its data, and then later downloading them into somebody else. Unethical but not impossible. Perhaps they can suppress erasing and pushing out any other memory of the subject transferred making them a host. Then through plastic surgery recreate the individual. Would you as an elite trust somebody else to do this. Haha it isn't quite there yet but it is being attempted. Or creating virtual avatars that completely mimic yourself in looks speech and actions. Some of this tech could also theoretically keep an aged dying elite in a coma, and create a neural link in order to otherwise massively extend life support where through a computer they could still be alive and function living indefinitely.

None of this explains the anomalies. Alternative life syndrome. Where people have been documented with remembering their former lives. Or even sometimes the same faces being seen in history at conflicting points.