The b12 in silk is from the makers adding the same B12 that gets put into pills. Last time I checked the pill form of b12 comes from big vats of bacteria (or yeast).
B12 deficiency is a problem of a freakishly clean environment. Dirty carrots, dirty water, the bacteria swarming on meat is where natural b12 comes from. Animals don't synthesize it anymore than we do.
ref: https://pubmed.ncbi.nlm.nih.gov/29216732/