I love what the guy is doing. It is a one-man experiment that would be very very hard to reproduce, or even get ethics approval and funding for, by a research lab. But on the other hand, I get a sense that the public side of his results are overblown. For example, my field is epigenetics, so I had a look at his "epigenetic clock" results. He uses "DunedinPACE" to track the rate of aging and his result is supposedly 0…
He does mention things like that. For one, he posted a link to this article: https://twitter.com/bryan_johnson/status/1721578475759239658....
He's also made a number of posts, often as replies to people asking the same sort of question that you are, pointing out that 95% of longevity is the simple things we're aware of (diet, exercise, etc.) and that he's just testing out all the other stuff because he can/he's interested/it's a worthwhile investment of time and money for him to get that last 5%.