MakeAppx/MakeMSIX and Desktop10:IconHandler

Microsoft documentation includes desktop10:IconHandler - Windows UWP applications | Microsoft Learn, a package level extension mentioned in desktop10:Extension (in Package/Extensions) - Windows UWP applications | Microsoft Learn .

I previously reported a documentation issue Missing elements · Issue #327 · MicrosoftDocs/winrt-related (github.com) regarding what appears to be three missing items in the documentation (one of which is for the IconHandler), both as elements and for the Category strings that likely are missing too.

I found that both MakeAppX (used in the MSIX Packaging Tool) and MakeMsix are aware of Desktop10 (at least when MaxVersionTested is set above 22000) and when run on a manifest including the IconHandler in a desktop10 package extension with category "windows.IconHandler" they result in an error that indicates that only the currently three categories are allowed.  Thus, it probably isn't just a documentation issue.

So:

• How do we use Desktop10:IconHandler,
• What OS versions is (/will it be) supported on,
• Is a product fix required.