Some people can be vegan and never take any vitamin supplements, other people can't. That the problem with diets and lifestyles what fits one won't fit another.
I work on a farm, I tan, I should be able to make my own Vit d. I can't and I'm on 5k daily in summer and 10k in winter. Gotta keep a eye on my folic acid and b12 too, and I'm on a pretty omnivore style diet. Almost all the meat I eat we either raised or hunted, veggies we try to go more organic but I live in Mississippi. We're lucky to have actually two grocery stores in the same small town.
My camp in all of this is this: If it works for you awesome, be it vegan or keto. Don't though go play doctor and berate people for not eating your way or attack people who politely bring up the flaws in said diets/lifestyles. I say polite because I know folks aint gonna be like that.