Samsung Galaxy S21 series to receive One UI 3.1.1 update in late August0
Although we don't know yet what major changes the next One UI update will bring to Galaxy devices, we do know that both Galaxy Z Fold 3 and Galaxy Z Flip 3 phones will ship with One UI 3.1.1 right out of the box.
Samsung Galaxy S21 series will be among the first to receive the One UI 3.1.1 update at the end of August.
A Samsung rep confirmed on the company's community forum that after the August security patch, the Galaxy S21 will receive the One UI 3.1.1 firmware around the end of the next month (via TizenHelp).
As far as the accuracy of the statement goes, it appears that this moderator only answers specific questions related to software updates when it had confirmation from Samsung's development team. The good news is we're likely to learn more about One UI 3.1.1 and its availability on older Galaxy devices as early as August 11.