The release date of 20.04.3 (26-August-2021) refers to the ISO release date for new downloads & installs.
It's normal for installed systems to get it days-weeks ahead of the date (a focal system has reported as 20.04.3 for over a week now if I recall correctly). This is expected; the RC for 20.04.3 has been out for a number of days now, and hopefully the current release-candidate will be the ISO that is released.
FYI: The initial planned date of release for 20.04.3 was actually 19-August-2021, but due to some SHIM & like issues (delayed so fixes could be implemented which is now all done !), the release has been pushed back a week (releases are always a Thursday) thus the longer period of .3 for installed systems before the ISO release date, than occurs some cycles.
For full details of the 20.04.3 release; check out the status tracker document.