N.B. Not to be confused with the second August update and Security patch... AUHB
This latest release is the 17th for the Global, Exynos, S21 series and is currently being rolled out by Samsung only 11 days after the second August update, AUHB which is still, currently, being rolled out.
As far as I can tell and from the, "S", in the Build number, this is just for the September Android Security patch on the previous, AUHB, update. Both CSC and Baseband are unchanged from AUHB.
As per post #1, TBC = To Be Confirmed, as I did a full, 7693MB, manual update and not an OTA.
Samsung update AUHD
As suspected by @GoanGeek, this update is merely the September Android Security patch.
I also tend to agree with @adamlee, that this quick release, so soon after the previous AUHB, indicates a readiness for the Android 12 Beta One UI 4.0 test firmware to be rolled out imminently.
What is your device's CSC code?