Yes, idli contains B12.
One can suspect of having vitamin B 12 deficiency if you are constantly feeling lethargic and having nausea along with stomach upset.
Research is suggestive that fat soluble vitamin D is deficient in people who have digestive tract disorders such as bowel disease because vitamin D along with dietary fats are not absorbed adequately.
The role of vitamin B 12 is very crucial as without enough red blood cells, your tissues and organs don't get enough oxygen. As a result your body cannot work well. You will suffer from weak musles, numbness and extreme fatigue.
This is because vegetarians and vegans are at a risk of vitamin B12 deficiency. Additionally, it has been reported that 1.5 to 15% people globally have vitamin B12 deficiency.