Hi AaronTudor,
I'm David, and I'm happy to help you.
As Windows Update is not installing this update, I suggest you install it using the Update Assistant. Microsoft has already released version 21H2, so the tool will update Windows to this version.
Download the tool from the link below.
https://go.microsoft.com/fwlink/?LinkID=799445
Source: https://www.microsoft.com/en-us/software-downlo...
I hope this helps. Feel free to ask back any questions.