The "1904x.1387" builds represent two parallel versions of Windows 10 updated in late 2021:
Introduced GPU compute support in the Windows Subsystem for Linux (WSL) and simplified passwordless deployment models for Windows Hello for Business . Significant Fixes in this Release windows 10 lite version 21h221h1 build 1904x1387 fixed
The "fixed" aspect of this build refers to several critical system resolutions provided by Microsoft: The "1904x
Key Features of Build 19043.1387 (21H1) and 19044.1387 (21H2) windows 10 lite version 21h221h1 build 1904x1387 fixed