Cherry picking one vitamin deficiency in vegans. Omnivores are deficient in other vitamins. The answer is supplementing, not changing foods you eat.
> Omnivores had the lowest intake of Mg, vitamin C, vitamin E, niacin and folic acid. Vegans reported low intakes of Ca and a marginal consumption of the vitamins D and B12.
> Omnivores had the lowest intake of Mg, vitamin C, vitamin E, niacin and folic acid. Vegans reported low intakes of Ca and a marginal consumption of the vitamins D and B12.
https://pubmed.ncbi.nlm.nih.gov/26502280/