Hi
I have had this problem for about 2 weeks then i found a solution
I downloaded the windows subsystem for android "Msixbundle" file from store.rg-adguard.net little did i know as the program was updated windows needed "Microsoft.UI.Xaml.2.6" and in some cases (not mine) "Microsoft.VCLibs.140.00.UWPDesktop" for the new versions to install them
so after spending a lot of time found out i should install the ".Appx" file of Microsoft.UI.Xaml.2.6 which i found in the website right above the subsystem file i downloaded.
seeing your error I'm guessing we have the same problem
so if that's your case you'll need to :
1 - go to store.rg-adguard.net
2 - either paste the Microsoft store link of the subsystem or change "URL" to "productid" and use (9P3395VX91NR)
3 - change "RP" to "Slow" and hit the check button
if you did all the above steps right you'll see a list of apps and subsystem will be at the end with .Msixbundle format.
To install Microsoft.UI.Xaml.2.6 you should download the right version for your system (x64 or x86 or arm … ) that ends in .Appx format and then install it by double clicking the downloaded file and clicking install.
After that you should be able to install the subsystem via Add-AppxPackage in PowerShell without any errors
that's it ! hope it helps