Apple has just released the update to bring Big Sur to version 11.4. This appears more modest in size, and for an M1 Mac is around 4 GB, or about 3.5 GB for an Intel model.
This update adds Apple Podcast subscriptions and channels, and fixes bugs with bookmarks in Safari, the display of websites after waking from sleep, export of keywords of images in Photos, Preview freezing when searching PDF documents, and 16-inch MacBooks freezing when playing Civilization VI. Full details are given here.
Details of security fixes are given here. They include five kernel bugs, several which could enable apps to break out of their sandbox, a bug in kext management which could allow the loading of unsigned kernel extensions, no less then five vulnerabilities in smbx, and six in WebKit. Apple warns that one bug, which allows a malicious app to bypass Privacy settings, may already be actively exploited.
Released at the same time are Security Updates to Catalina (2021-003) and Mojave (2021-004). Release notes for Catalina are here, and for Mojave are here. Both are long, and clearly these are important security updates for those still using those older versions of macOS.
I will post further details here as I get them.