Apple has released a further update to Big Sur, aimed primarily at some MacBook Pro 2016 and 2017 models, where it fixes a serious problem in 11.2 which could prevent the battery from charging.
As usual with Big Sur, this update is only available through Software Update (and
softwareupdate), and is still large at around 2.3 GB for Intel Macs and 3.4 GB for M1 Macs.
It’s accompanied by macOS Catalina 10.15.7 Supplemental Update* (note the asterisk) and macOS Mojave 10.14.6 Security Update 2021-002, which bring security updates, of which the most notable fixes the recently-reported ten-year-old vulnerability in
sudo. The Big Sur and Catalina updates also fix a couple of vulnerabilities in the Intel Graphics Driver. Security release notes are already here.
Standalone updaters are now available for Catalina Security Update 2021-001 from here, and “macOS Catalina 10.15.7 supplemental update” (which Apple also refers to as Security Update 2021-001!) from here.
This update doesn’t update the firmware in Macs with T2 chips. However, it downgrades MRT to version 1.72. Once you’re logged back in, it’s worth checking that Software Update has updated that again to 1.73, which is the current version.