Samsung has been rolling out the One UI 6 update for Galaxy devices at lightning speed since late October, and the company seems to be equally passionate about the December 2023 security update.
Several Galaxy phones have received the One UI 6 update and the December 2023 security update in quick succession over the last few days. The Galaxy S21, S21+, and S21 Ultra are on the list as well, at least in the US, where the 2021 flagship trio was updated to One UI 6 two weeks back and is now being updated with the latest security patch.
The December 2023 update is rolling out to factory-unlocked and carrier-locked units (including those on Verizon's network) at the same time. Like other Galaxy devices, the Galaxy S21 series is only being treated to security fixes with the December update.
The latest security patch fixes 75 security vulnerabilities, seven of which are deemed critical, in Android and Samsung One UI. It also fixes vulnerabilities in smartphones powered by select Exynos chips, but those don't apply to the Galaxy S21, S21+, and S21 Ultra sold in the USA.
To download the December update on your Galaxy S21, S21+, or S21 Ultra, open the phone's Settings app, navigate to Software update, and tap Download and install. Try doing that a few times or wait a few hours to check again if the update doesn't show up on the first attempt.