How can we use ThemeResource in markup extensions

[HO-COOH]

For example, with the usual FontIcon, I can use

<FontIcon Glyph="&#xE102;" FontFamily="{ThemeResource SymbolThemeFontFamily}"/>

But using the FontIconExtension in the toolkit,, this gives me exception

<AppBarButton Icon="{ui:FontIcon Glyph=&#xE102;, FontFamily={ThemeResource SymbolThemeFontFamily}}" Label="Using FontIconExtension" />

Output:

22:49:03:129	WinRT information: Failed to assign to property 'CommunityToolkit.WinUI.FontIconExtension.FontFamily'. [Line: 14 Position: 19]
22:49:03:129	The text associated with this error code could not be found.
22:49:03:129	
22:49:03:129	Failed to assign to property 'CommunityToolkit.WinUI.FontIconExtension.FontFamily'. [Line: 14 Position: 19]

I guess in order to support ThemeResource the property needs to be a DependencyProperty, but the base class MarkupExtension is not, so it's not possible this way?

The gallery app should have mentioned this issue