https://www.youtube.com/@KenDBerryMD

Which one? You can easily find both Berry's and Berg's channels on youtube by looking by their names, Elevate Brain Training doesn't seem to be a channel but some sort of app for phones.

Both Berry and Berg also have sites outside YT. Shawn Baker is another carnivore diet promoter I know besides Berry, an orthopedic surgeon.

I haven't looked that deeply on the differences between keto and carnivore when it's a question which would be better, or low carb in general, but I'd think that at least carnivore might be easier to stick to as the main rule is simply "all animal products, no plant ones" instead of lists of what plants you can and cannot eat.

I haven't been able to find all that many disaster stories about carnivore, although it seems that for some people with specific diseases it's not good, like people who have something called familial hypercholesterolemia (FH). But mostly you can find only warnings about what it might cause instead of proofs it has caused those things for some individuals, while there seems to be a lot of success stories about carnivore eating, including people who have been on that diet for years, maybe decades, and more stories of people who have been on some version of low carb or keto for decades as those have been promoted longer, and who are still healthy.