MS Store error 0X80073D21

Hello Tyler Holland, welcome to Microsoft Q&A forum.

The error message clearly says “the app must be installed to the system drive”, but I don’t see you mention explicitly checking that. Have you confirmed that the install location for new apps is set to the C: drive and tried installing there? Even if Windows itself is installed on C:, this setting can point to another drive, and the Store uses this setting for app installs.

If not, please do this first: Go to Settings > System > Storage > Advanced storage settings > Where new content is saved, and under “New apps will save to”, make sure it is set to C: (your system drive). After that, retry installing the app from Microsoft Store.

If you have already done that and the error persists, the PowerShell message indicates that the Microsoft Store components are compromised. The only supported way to restore the Store in this situation is to reset or reinstall Windows.

• Download the latest Windows 11 ISO from Microsoft’s official site.
• Run setup.exe from the ISO.
• Choose Keep personal files and apps.
• Complete the installation. This will restore Microsoft Store and other system components without wiping your data.

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 Get-AppxPackage *Microsoft.WindowsStore* -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$_.InstallLocation\AppXManifest.xml"}

Attempted the above in powershell per the AI answer and received

Add-AppxPackage : Cannot find path
'C:\WINDOWS\system32\Microsoft.WindowsStore_22511.1401.5.0_x64__8wekyb3d8bbwe.InstallLocation\AppXManifest.xml'
because it does not exist.
At line:1 char:64
+ ...  | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$_.Ins ...
+                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : ObjectNotFound: (C:\WINDOWS\syst...ppXManifest.xml:String) [Add-AppxPackage], ItemNotFou
   ndException
    + FullyQualifiedErrorId : PathNotFound,Microsoft.Windows.Appx.PackageManager.Commands.AddAppxPackageCommand