According to the latest reports, owners of the Galaxy S21, Galaxy S21+, and Galaxy S21 Ultra in Germany will receive this update on the build numbers G991BXXS5CVHI, G996BXXS5CVH1, and G998BXXS5CVH1. We expect it to be available in more European countries and regions within a few days. As of now, Samsung has not detailed the September 2021 security patch as to which security and privacy vulnerabilities are getting patched. The changelog for Galaxy S21 series does not show other changed apart from improved device security and stability. Samsung Galaxy S21 series in the specified regions have already started receiving the September 2021 security update. To manually check for the new update, just go to Settings » Software updates and then check for new updates.
Samsung released the Galaxy S21 series earlier this year with Android-11 based One UI 3.1 on board. Recently, a Samsung community member confirmed that Galaxy S21 series will soon get One UI 4.0 which is based on Android 12. The exact timeline is currently unknown, but the company may start One UI 4.0 beta on the S21 series as early as next month. source
