Well again, what's the actual use case for this? Is there any developer who distributes .appx archives directly?
On the winget community repository, there are a lot of packages distributed as msix/appx: https://github.com/search?q=repo%3Amicrosoft%2Fwinget-pkgs+%22InstallerType%...
Winget also officially [supports installing apps from the Windows Store](https://learn.microsoft.com/en-us/windows/package-manager/winget/source), which requires appx support as well.
Outside of winget, there are projects that also release Windows builds as an appx package. Kiwi comes to mind, it recommends that users use the appx: https://github.com/kiwix/kiwix-js-pwa/releases/tag/v3.7.1