https://www.healthline.com/nutrition/impossible-burger#what-...
The Impossible Burger is supplemented with a ton of B vitamins (for thiamine, several weeks' supply).
Most vegans eat lots of other B containing foods, including yeast (which is after all how plant-eating animals manufacture B vitamins in the first place, by fermentation during digestion). But for those who want to get it along with their protein source, the plant-based meat-simulacra also contain it.
It’s incredibly difficult to get sufficient quantities of B12 outside of meat products or manufactured supplements.
So either way your B12 is coming from supplements. It's either in a pill already, or the flesh of animal who didn't want to die, and they simply took the pill on your behalf.
Most nutritional yeast is supplemented with B12. It's a good source of protein and other minerals.
Many vegetarians also eat fermented pickles that contain B12 naturally, though you do have to eat rather a lot to get sufficient B12.
By contrast, most non-vegetarians are very deficient in fiber, and nobody ever seems to bother about it.