Migrate project from .NET Framework 4.5 to .NET Standard 2.0

I've got a .NET Framework 4.5 project and I want to migrate it to .NET Standard 2.0.

When I try to open this project a windows pops up telling me project is targeting .NET Framework 4.5 and it's no longer supported. It also requires that I update the target to .NET Framework 4.8 or I download .NET Framework4.5 directly from the browser. Otherwise, I can't load the proyect.

But I don't want to do either of those.

Searching on the internet I found that you just have to update .csproj, choose "netstandard2.0" as the TargetFramework and update packages with NuGet.

So my .csproj was something like this:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
<PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProjectGuid>{756DBCF8-3349-4CAE-B58C-47B7998BE3FF}</ProjectGuid>
    <OutputType>Library</OutputType>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>Wke.Cms</RootNamespace>
    <AssemblyName>Wke.Cms</AssemblyName>
    <TargetFrameworkVersion>v4.5</TargetFrameworkVersion>
    <FileAlignment>512</FileAlignment>
  </PropertyGroup>
...
More below
...

and I simply made this small change opening the file on my file explorer:

<?xml version="1.0" encoding="utf-8"?>
<Project ToolsVersion="15.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
  <Import Project="$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props" Condition="Exists('$(MSBuildExtensionsPath)\$(MSBuildToolsVersion)\Microsoft.Common.props')" />
  <PropertyGroup>
    <Configuration Condition=" '$(Configuration)' == '' ">Debug</Configuration>
    <Platform Condition=" '$(Platform)' == '' ">AnyCPU</Platform>
    <ProjectGuid>{756DBCF8-3349-4CAE-B58C-47B7998BE3FF}</ProjectGuid>
    <OutputType>Library</OutputType>
    <AppDesignerFolder>Properties</AppDesignerFolder>
    <RootNamespace>Wke.Cms</RootNamespace>
    <AssemblyName>Wke.Cms</AssemblyName>
    <TargetFramework>netstandard2.0</TargetFramework>
    <FileAlignment>512</FileAlignment>
  </PropertyGroup>

Changed "TargetFrameworkVersion" for "TargetFramework" and put "netstandard2.0"

Now I can load the project, but if I try to open project properties I get the following error:

12/04/2024 10:42:18
Recoverable
System.ArgumentException: Expected 1 values for property Build::DefineConstants, but got 0. The property page may not be defined for all configurations.
Nombre del parámetro: values
   en Microsoft.Requires.Argument(Boolean condition, String parameterName, ValidationInterpolatedStringHandler& message)
   en Microsoft.VisualStudio.ProjectSystem.VS.Implementation.PropertyPages.Designer.Property.Update(ImmutableArray`1 values)
   en Microsoft.VisualStudio.ProjectSystem.VS.Implementation.PropertyPages.Designer.Property..ctor(PropertyMetadata metadata, ImmutableArray`1 values, PropertyContext context, ImmutableHashSet`1 varyByDimensions)
   en Microsoft.VisualStudio.ProjectSystem.VS.Implementation.PropertyPages.Designer.PropertyContextFactoryBase.ToProperty(IUIPropertySnapshot property, Page page, Category category, Int32 order, PropertyContext propertyContext, IPropertyEditorRegistry propertyEditorRegistry)
   en Microsoft.VisualStudio.ProjectSystem.VS.Implementation.PropertyPages.Designer.ProjectPropertyDataAccess.Observer.<HandleDataAsync>g__CreateProperties|14_5(<>c__DisplayClass14_0& )
   en Microsoft.VisualStudio.ProjectSystem.VS.Implementation.PropertyPages.Designer.ProjectPropertyDataAccess.Observer.<HandleDataAsync>g__ProcessInitialData|14_1(<>c__DisplayClass14_0& )

Tried to google it and found this, but didn't work for me.

What am I missing here? Do I need to make more changes? Any help is more than welcome.

It is probably the easiest to upgrade your csproj to the new syntax. Your csproj is now still in the old style, which complicates things. Try updating it and re-add your nugets and references again and you should be good to go.

Your csproj should look something like this:

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <RootNamespace>Wke.Cms</RootNamespace>
    <AssemblyName>Wke.Cms</AssemblyName>
    <TargetFramework>netstandard2.0</TargetFramework>
  </PropertyGroup>

</Project>