The base build number for that original release, with early preview builds like 22000.51 appearing in June 2021 (which corresponds to the 06/21 timeframe).
The Windows 11 version 21H2 update history on Microsoft Support catalogs every build from the initial launch through its end of service. Search results for Windows 11 (2105)
There is no official release of Windows 11 under the version name This number appears to be a combination or a slight mislabeling of two separate milestones in Windows 11's early history: The base build number for that original release,
You may be thinking of Windows 10 version 21H1 (May 2021 Update), which was released just before Windows 11 was announced. released in October 2021.
The original launch version of Windows 11, released in October 2021.