Apple has made a strange change in the handling of Mac OS updates, without warning or explanation. Mr Macintosh was first with the discovery, which then has reported by Howard Oakley at Eclectic Light Co.
What it’s about is the standalone update packages Apple has always previously posted on its support pages, so-called delta and combo updates. Not a single update for Mac OS 11 Big Sur has been posted.
This used to be the recommended way to update Mac OS at a time when updates were relatively common. This has not been the case for a long time, and Big Sur has a new system architecture where only fully installed updates are retained.
Why Apple has not released standalone service packs is unknown, and the change may make it for many users who, for example, have multiple Macs and slow Internet or have Macs that can not or may not connect to the Internet. This applies, for example, to some authorities and companies that work with sensitive things.
You can still download the Big Sur installer from the Mac App Store and save a copy of it. When you run it, you can install it over your existing system, which acts as an update. But the program is 12 GB. By comparison, the delta update of 10.15.7 is 1.2 GB and the combo update is 2.9 GB.