The Galaxy A51 has been a very sucessful midranger, providing very good specs at an even more competitive price point. The phone had done extremely well in sales, attracting over a million consumers to it.
The Galaxy A51 was released almost 2 years ago and has been enjoying quarterly updates, with the latest being the February security patch.
Unfortunately Samsung has now decided to make this update biannual. Which means users of the A51 can only hope to get an update every 6 months.
The good newsbis, since the A51 is eligible for the Android 12 One Ui 4.0 update, they will be pushing it out as early as next week. But this may not be for all regions at once. The A51 will continue to get updates for 3 years from date of release as well.
You should note that the A51 5G still is on the quarterly schedule until further notice.
Samsung has not provided an official statement as to the reason of the update schedule downgrade. It is encouraged for the A51 users to accept this as the new norm and carry on.