How to resolve CS0433 error when building WindowsAppSDK 1.5.X solutions after Visual Studio update?

[LegendaryBlair]

Description

After updating Visual Studio, building a project using WindowsAppSDK 1.5.X results in the following error: 'error CS0433: The type 'TextDecorations' exists in both 'Microsoft.WinUI, Version=3.0.0.0' and 'Microsoft.Windows.SDK.NET, Version=10.0.19041.38'. This issue prevents the project from building successfully. How to resolve this issue?

Related issues

#4788

[LegendaryBlair]

Root cause

The error occurs due to a recent Windows SDK projection update that added some Windows namespace types, including TextDecorations, which overlap with types in the Microsoft namespace. This causes a conflict when building projects using WindowsAppSDK 1.5.X.

Solution

To resolve this issue, you can either update to WinAppSDK 1.6 or above, which addresses this conflict, or specify an older Windows SDK projection version in your project file.
To specify an older version, you will need to add the WindowsSdkPackageVersion property to your csproj to lock the Windows SDK projection version to 34. Let's say your project is targeting at Windows 10.0.19041.0, then set the property as the following.

<PropertyGroup>
  <WindowsSdkPackageVersion>10.0.19041.34</WindowsSdkPackageVersion>
</PropertyGroup>

Once you are able to move to WinAppSDK 1.6 or above, you should remove this property.