On systems where the App Installer update cannot be deployed using the Internet-based installer, Microsoft also provides an offline version on the Microsoft Download Center (download link).

Enable Developer Mode Check App Package Compatibility Check for Trusted Certificates Use PowerShell to Install App Package Update C++ Redistributable and .NET Framework Packages Check App ...

If not, you'll need to install App Installer from the Microsoft Store, which comes bundled with WinGet. If you prefer, you can instead install WinGet from its GitHub repository.

Microsoft has disabled the MSIX ms-appinstaller protocol handler exploited in malware attacks to install malicious apps directly from a website via a Windows AppX Installer spoofing vulnerability.