So no, people don’t need meat. Not for B12, or for proteins or for iron or for anything else.
Do people want to eat meat? That’s a different story.
I take a big multivitamin in the evening and that’s it.
Something people frequently overlook (or are unaware of) is that in much of the world, animal agriculture utilizes B12 supplementation. This is part of why there is B12 in commercial animal products. Without that, B12 levels in commercial animal products would be lower. Further, people who eat animal products aren't guaranteed to avoid deficiencies.
The idea that we "need" meat is thoroughly debunked by decades of excellent, high-quality research. What we "need" as far as B12 goes is essentially less sanitary environments; we (and animals we ate) used to get enough from food and water which wasn't clean by current standards.