Ok, I have a problem here, the 21H1 update installed just fine, but then later on that day I got an optional update for the 21H1 *preview*, which is odd, that never came before the official update.
This is normal. For stable releases, an optional quality update is released every 4th week of the month(known as D release). Regular updates go out on the 2nd Tuesday of the month.
Windows 10 update servicing cadence - Microsoft Tech Community
- The “C” and “D” releases occur the third and fourth weeks of the month, respectively. These preview releases contain only non-security updates, and are intended to provide visibility and testing of the planned non-security fixes targeted for the next month’s Update Tuesday release. These updates are then shipped as part of the following month’s “B” or Update Tuesday release.