Samsung is currently sending the October 2021 security update to Galaxy S21 / S21+ / S21 Ultra in specific regions, including Germany, India, and the Philippines. It can be identified by the firmware version G991BXXU3AUIE. The new OTA update also improves the stability of functions. Since the October 2021 security patch rollout has just got started, the details about vulnerabilities getting patched are currently unknown. We can expect Samsung to reveal the details in the first or second week of the month.
Samsung Galaxy S21 series users in the specified regions should receive an update notification in the coming days, if not received yet. We can expect the update to start hitting other areas in the next few days. Samsung is also in the works to bring Android-12 based One UI 4.0 beta update soon. Galaxy S21 series users are lucky, as they will be the first from Samsung to see what’s new in One UI 4.0 and Android 12. [source]