You might be surprised to see May 2021 security patch rolling out in April end, but it’s not surprising for Samsung, as they have done this many times in the past. The May 2021 security update for Galaxy S21 series is currently rolling out in Europe with firmware version G99xBXXU3AUDA.
Samsung has not detailed the May 2021 security patch but as usual, it will fix multiple CVE’s (Common Vulnerabilities and Exposures) to enhance system security. In addition to a new security patch, the changelog also mentions improvements to camera performance and Quick Share.
This is a bulky update and requires 1150MB of internet data. So, it is recommended to download the package over a Wi-Fi connection. Galaxy S21 users in Europe who have not received the update yet can manually check the status by navigating to Settings » Software updates.
[source | via]