From personal experience, nutritional yeast / flavour yeast enriched with B12 (it’s produced by bacteria, the rest of the B group vitamins are yeast-originating) works. Upon testing, repeatedly, I’ve had normal levels of B12. My average dose is a spoonful per day on some or another food.

Since around 3 years I use a toothpaste with B12 and just checked my blood last week: Perfectly good levels of B12.