I can confirm this. My partner (vegetarian and world's fussiest eater since childhood) was so unwell a few months ago. He had been feeling off colour for a while, and suddenly went downhill fast, it was a nightmare trying to get help as it was the height of the pandemic. Long story short, he had severe anaemia, was in ITU care, needed several blood transfusions over his two week stay in hospital. He had short term memory loss for only a couple of days before he was finally admitted to hospital, but he still has memory loss even though his blood is back to normal
I think anyone following a vegan or vegetarian diet (myself included) should be really careful, and keep an eye on your B12 and folic acid levels if you can. The damage caused by anaemia is shocking.