Yes, I believe you need a varied diet, vegan or not. In a vegan diet, you also need B12 supplements because it's absent* in a vegan diet and it is an essential

Yes, I believe you need a varied diet, vegan or not. In a vegan diet, you also need B12 supplements because it's absent* in a vegan diet and it is an essential nutriment. Lacking B12 is bad. *except B12-enriched food if you happen to have it, but you still need to make sure your B12 intake is okay.