Windows 10 21H1 (19043) is on the verge of final rollout with KB4598291. This new version in 21H1 is supposed to be 19043.782.
To install Windows 10 21H1 all you need is to install KB4598291 but before starting this procedure don’t forget to take a backup. You have to run a few commands (given ahead), which will activate the Windows 10 21H1.
KB4598291 Windows 10 2004 19041.789 and 20H2 19042.789
To check out the version and build, open Winver or go to Settings => System =>Windows Specifications. You will notice that you are on the way to get Windows 10 Version 21H1 (build 19043). Here are the command-lines –
Dism /Online /Add-package:C:WindowsservicingPackagesmicrosoft-windows-product-data-21h1-ekb-package~31bf3856ad364e35~amd64~~10.0.19041.789.mum
Dism /Online /Add-package:C:WindowsservicingPackagesmicrosoft-windows-product-data-21h1-ekb-wrapper-package~31bf3856ad364e35~amd64~~10.0.19041.789.mum
Dism /Online /Add-package:C:WindowsservicingPackagesmicrosoft-windows-updatetargeting-clientos-21h1-ekb-package~31bf3856ad364e35~amd64~~10.0.19041.789.mum
Dism /Online /Add-package:C:WindowsservicingPackagesmicrosoft-windows-updatetargeting-clientos-21h1-ekb-wrapper-package~31bf3856ad364e35~amd64~~10.0.19041.789.mum
Now onwards, all future updates will be installed in the same way as for Windows 10 2004 or 20H2. This one LCU update is now for three Windows 10 versions.
Source – Deskmodder.