I've worked with one person who was fine on 3-4 hours a night. He'd go to bed with the rest of his household, get up 3-4 hours later, go back to engineering or reading a book. He told me he had family members with similar sleep needs, so probably genetic. I know there are some of us 'normals' who try to get by on short sleep - but they mostly show effects after a week. Saw none of that in this guy, who'd been doing it (according to him) 'since he was a kid'. daVinci sounds much more extreme. I’d guess he had similar genetics and was pushing himself.

Given what we now know about the glial system (and glymphatic waste clearing during deep sleep) I have to wonder how he's doing these days as that was 20ish years ago... OTOH, from studies on sleep deprivation, particularly ones on depriving subjects of a particular ‘stage’, when the subjects were allowed to sleep normally, they’d immediately ‘make up’ the stage they’d been deprived of, so if you’re not feeling a physiologic ‘need’, you’re probably fine.

All that said, you’re right to be concerned. Both Ronald Reagan and Margaret Thatcher boasted of not needing much sleep — and both died with dementia.