XamlC error XC0009 with CommunityToolkit.Maui.Popup with Dotnet 9 Preview 5

[rogerbriggen]

Description

I get a compile error if I use a CommunityToolkit.MAUI popup.
This works in dotnet 8 and dotnet 9 pre 3 so it seems to be newly introduced.

This bug is for dotnet 9 preview 5 which does not exist in the version drop down below.

Steps to Reproduce

1. Fetch project from https://github.com/rogerbriggen/MauiDotNet9Pre5_Popup
2. Try to compile this very simple project
3. -> XamlC error XC0009: No property, BindableProperty, or event found for "Content", or mismatching type between value and property.

Link to public reproduction project repository

https://github.com/rogerbriggen/MauiDotNet9Pre5_Popup

Version with bug

9.0.0-preview.4.10690

Is this a regression from previous behavior?

Yes, this used to work in .NET MAUI

Last version that worked well

9.0.0-preview.3.10457

Affected platforms

iOS, Android, Windows

Affected platform versions

No response

Did you find any workaround?

No

Relevant log output

1>C:\Program Files\dotnet\sdk\9.0.100-preview.5.24307.3\Sdks\Microsoft.NET.Sdk\targets\Microsoft.NET.RuntimeIdentifierInference.targets(314,5): message NETSDK1057: Sie verwenden eine Vorschauversion von .NET. Weitere Informationen: https://aka.ms/dotnet-support-policy
1>Analysetools werden übersprungen, um den Build zu beschleunigen. Sie können den Befehl „Build“ oder „Rebuild“ ausführen, um Analyzer auszuführen.
1>O:\DatenP\Programmieren\repos\MauiDotNet9Pre5_Popup\MauiDotNet9Pre5_Popup\SimplePopup.xaml(6,6): XamlC error XC0009: No property, BindableProperty, or event found for "Content", or mismatching type between value and property.

[TheresasAccount]

This is also a problem for me, I am also using expanders and when trying to fill out the Header:

[Redth]

Duplicate of #22975