This specific string refers to a of Windows 10, often found on file-sharing or torrent sites. It is not an official Microsoft release but rather a modified ISO image compiled by independent contributors (frequently a group or individual known as "Generation2"). Breakdown of the Version Details Windows 10 update history - Microsoft Support
* Windows 10, version 21H1 update history. * End of service statement. * KB5021233 (OS Builds 19042.2364, 19043. Microsoft Support