Unless you have full access to someone's medical chart and/or in the examining room with the patient, it's mostly detective work. And sometimes, even that's not enough. You need information to make a theory and then to prove it.
My father died of a partially dissected aorta, a slow bleed into the chest. I had to extrapolate this with the help of his cardiologist opining that his symptoms of a backache sounded like the aorta theory; same with my cousin, who's also a cardiologist. How did the aorta become separated? My father rear-ended a van at the gas pumps. No air bag. Refused to be examined at a hospital. Didn't go to any of his doctors. Kept it a secret from all his children.
Found out about the accident when his traffic offense tickets came in the mail one week after his death.
I inspected his car with an insurance investigator. We found that the brake pedal was very worn at the right lower corner. And we were fortunate that we found a pair of Dad's shoes in the back seat. The worn part of the brake matched the shoe. Because of the layout of the brake and accelerator pedals, Dad had been driving, using the corner of the brake to stop, not the full pedal. And his foot slipped from the brake to the accelerator, causing his car to heavily bump into the van. And his chest hit the steering column. Being 92 at the time, that was enough to partially dislodge his aorta from his heart.
I didn't have to know how Dad died, but I wanted to know all the same.
Back to Trump. We're all speculating and any guess is good as the next. I trust RFK, Jr. will seal his death certificate.