Samsung used to have a very bad rep for updates going out to its unlocked smartphones sold in the US, and while the situation has improved somewhat, it's still not great. Case in point: the unlocked US-bound Galaxy A51 is now starting to receive the update to Android 11 with One UI 3.1 on top.
That's all fine and dandy, until you remember that international units got Android 11 back in February. That's about four months of delay right there for you yanks. Anyway, the new Android version from 2020 is finally on its way to you now.
It arrives over the air as build version A515U1UEU5CUF1 and includes the June 2021 security patch level. It should make its way to all unlocked Galaxy A51 units sold in the States in due course, but in the meantime, if you're impatient, you can always go to Settings > Software update and manually check if it's available for you. Who knows, maybe you'll get lucky.