There’s been a lot of back-and-forth. B12, like iron and Protein, are digested differently by the gut (with different efficiency) based on how they are consumed.
If absolutely all you care about is nutrition and nothing else, you should be eating a small amount of non-processed red and white meat (and/or seafood) on a regular basis because it is the best and healthiest source of those three things. Key term “small amount”