yeah the whole b12 thing is just overblown. obviously its best to take a supplement but even the human gut bacteria can produce b12, so its not really the best argument

A quote from this

"Vitamin B12 Supply through Gut Bacteria
Strains of bacteria found in a healthy human intestine can produce vitamins B1, B2, B5, B6, folate, B12 and K2 and probably also contribute to the supply of these nutrients (5, 6).
In animals, this has been recognised for much longer: ruminants have a special compartment in their stomach, known as the rumen, in which bacteria can produce B12. This is why cows only need a sufficient dietary supply of the trace element cobalt, which bacteria require for B12 synthesis, in order to produce their own supply of the vitamin (7).
The same also applies to fish, for example, which also need cobalt but no dietary B12, as they produce their own supply of the vitamin through symbiosis with bacteria (8, 9). This ability explains why many herbivore species do not require B12 in their diets
It has long been assumed that human intestinal bacteria do not contribute in the same way to the supply of B12, since production of the vitamin takes place mainly in the large intestine, where it can no longer be absorbed. In the 1980s, however, it was shown that B12-producing bacteria also live in the small intestine (10, 11).
Surprisingly, this area has hardly been researched since then and there is a lack of studies on the ideal contribution of intestinal bacteria to the B12 supply. The fact that some long-term vegans, who do not have any B12 sources in their diet, do not suffer from vitamin B12 deficiency suggests that the body’s own supply through gut bacteria might be possible. However, it has not yet been researched as to whether these people might actually be surviving from previously created B12 stores."