Maybe GitHub Actions hosted runners are using an old version of Visual Studio, MSBuild, or the .NET SDK, because not only are extension blocks broken, but now the field keyword requires Preview C# language version. Didn't .NET 10 come out 5 months ago? Why is this still a problem?

Author: Aldaviva

WinampNowPlayingToFile/WinampNowPlayingToFile.csproj

@@ -11,16 +11,12 @@
     <RootNamespace>WinampNowPlayingToFile</RootNamespace>
     <AssemblyName>WinampNowPlayingToFile</AssemblyName>
     <TargetFrameworkVersion>v4.7.2</TargetFrameworkVersion>
-    <LangVersion>latest</LangVersion>
+    <LangVersion>preview</LangVersion>
     <FileAlignment>512</FileAlignment>
-    <FileUpgradeFlags>
-    </FileUpgradeFlags>
-    <UpgradeBackupLocation>
-    </UpgradeBackupLocation>
     <OldToolsVersion>3.5</OldToolsVersion>
-    <TargetFrameworkProfile />
     <RestorePackagesWithLockFile>true</RestorePackagesWithLockFile>
     <RuntimeIdentifiers>win;win-x64;win-x86</RuntimeIdentifiers>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>
@@ -31,7 +27,6 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <Prefer32Bit>false</Prefer32Bit>
-    <Nullable>enable</Nullable>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Release|AnyCPU' ">
     <DebugType>embedded</DebugType>
@@ -41,13 +36,8 @@
     <ErrorReport>prompt</ErrorReport>
     <WarningLevel>4</WarningLevel>
     <Prefer32Bit>false</Prefer32Bit>
-    <Nullable>enable</Nullable>
     <DebugSymbols>true</DebugSymbols>
   </PropertyGroup>
-  <PropertyGroup>
-    <StartupObject>
-    </StartupObject>
-  </PropertyGroup>
   <PropertyGroup>
     <ApplicationIcon>winampIcon.ico</ApplicationIcon>
   </PropertyGroup>