Samsung has already started rolling out the February 2021 Security patch update. Now the Galaxy S21, Galaxy S21+, and Galaxy S21 Ultra getting the update. Previously the Galaxy S20 series, Galaxy Note 20 series, and Galaxy A50 received as well.
The latest update of Galaxy S21, Galaxy S21+, and Galaxy S21 Ultra brings the February 2021 security patch and it identifies via firmware version G9910ZHU1AUAE, G9960ZHU1AUAE, and G9980ZHU1AUAE respectively. The firmware update has yet to be released for the international variants but it is now rolling out for the Galaxy S21 series in Hong Kong.
The latest update changelog is fairly generic, mentioning performance improvements, camera improvements, and other unspecified bug fixes.
If you own Galaxy S21, Galaxy S21 Plus, and Galaxy S21 Ultra so you can check the software update, Just tap on the Settings menu > Software Update > If available for your region, tap on Download and Install.