Stupid but genuine q- can you explain what you mean by- "We are very clean with our food and water, so our plant foods and water are mostly devoid of B12 " What

Stupid but genuine q- can you explain what you mean by- "We are very clean with our food and water, so our plant foods and water are mostly devoid of B12 " What if we didn't sterilize? Would the bacteria then produce it in our stomach? Once I "get " those bacteria in, do I have to replenish? Or you mean I have to eat those microbes as they themselves contain b12? In which case dead or alive, what does it matter?