Seriously? Tons of vegan foods have added B12 nowadays. If you're in doubt about your B12 levels you can always take a vitamin pill - recommended for most people anyway, due to low nutrient levels in most modern diets. The only reason anyone would need a B12 injection is if their body was incapable of absorbing B12 from the blood - a condition which is just as prevalent in meat-eaters and lacto-vegetarians as it is in vegans. As for plant-based foods having 'no Omega 3'... another misconception, I'm afraid. There are readily available sources of vegan Omega 3. If there weren't, then people like me, who've been vegan for 30 years, 40 years, 50 years... we wouldn't be here talking about these things, would we? We'd all be dead.
I don't know about 100 years ago - I'm not Amish so I don't limit my lifestyle to how people lived in the past. Nor do I live in Africa (although I hear from plenty of vegans who do live in Africa and they seem to be thriving). What I do know is that in 2022 in most Western countries veganism is a healthy and ethical option... and the ONLY option if we want to survive, according to top climate scientists