But my phone is in january security patch

More specifically, the beta program appears to have been opened briefly for Galaxy M31 and Galaxy M32 customers in India before Samsung closed the sign-up window, presumably due to high demand. The beta update for the Galaxy M31/M32 has firmware vers...

It may be for limited users.

Samsung A51 will get android 12 from april 2nd week onwards

Samsung M31 models will get android 12 updates from may 2nd week onwards.