installing WSL Ubuntu: Add-AppxPackage fails, "The Visual Elements extension failed while processing the Notification element"

Question

I want to install WSL 1 in my Win 10 OS, and have followed the instructions at https://docs.microsoft.com/en-us/windows/wsl/install-win10

1. from PowerShell as Admin: dism.exe ... - no problem
2. installing Linux distro (Ubuntu 20.04) via Microsoft Store fails as my IT services has disabled MS Store on my device
3. I therefore follow the instructions at https://docs.microsoft.com/en-us/windows/wsl/install-manual
4. from PowerShell as Admin, Add-AppxPackage ... now fails with the following error:

Deployment failed with HRESULT: 0x80073CF6, Package could not be registered. error 0x80070002: The Visual Elements extension failed while processing the Notification element.

See https://github.com/MicrosoftDocs/WSL/files/4798677/log.txt for the full log file.

Any thoughts on troubleshooting appreciated.