If I eat a flexitarian diet like Okinawans, Japanese, & some Africans do will I avoid b12 deficiency like they do? Or do they have B12 deficiency?

Animal protein. I do not know what these diets are. To have adequate intake of B12 you need to consume animal protein, keeping in mind that milk is an animal protein. For good health - Have a diet rich in fresh vegetables, fruits, whole grains, low fat milk and milk products, nuts, beans, legumes, lentils and small amounts of lean meats. Avoid saturated fats. Exercise at least 150 minutes/week and increase the intensity of exercise gradually. Do not use tobacco or alcohol in any form. Practice safe sex.
As far as I. know the only thing connected to this new "FAD" diet is "long life"... I personally think most of these "wonder diets" are JUNK SCIENCE My opinion only! Dr Z PS Vit B def is probably ubiquitous (everyhwere including Oklinawa!