Samsung Galaxy M51 is on quaterly security update list, so you will recieve security updates at an interval of 3 months. Currently, as far as I know, November security patch is rolling out for M51. Kindly go through the link https://security.samsungmobile.com/workScope.smsb
Please don't be so impatient about updates. Samsung is pushing update to M51 region-wise, when it's time for us, we will definitely get it.