I have installed VSCode, the C# extension for VSCode, via the extensions panel. I then installed .NET 5.0 from the Microsoft website. Finally, I installed the Unity hub and Unity. Unity booted I went into the Preferences menu (a submenu within Edit) and in External Tools set the script editor to Visual Studio Code. I started following a tutorial to learn the basics, but when I created a script and opened it in VSCode I got the following error messages in the OmniSharp log:

[fail]: OmniSharp.MSBuild.ProjectLoader
        The reference assemblies for .NETFramework,Version=v4.7.1 were not found. To resolve this, 
        install the Developer Pack (SDK/Targeting Pack) for this framework version or retarget your 
        application.
You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks
[warn]: OmniSharp.MSBuild.ProjectManager
        Failed to load project file 'c:\Users\richa\BrackeysTutorial\Assembly-CSharp.csproj'.
c:\Users\richa\BrackeysTutorial\Assembly-CSharp.csproj
c:\Users\richa\.vscode\extensions\ms-dotnettools.csharp-1.23.9\.omnisharp\1.37.7-
beta.23\.msbuild\Current\Bin\Microsoft.Common.CurrentVersion.targets(1180,5): Error: The reference 
assemblies for .NETFramework,Version=v4.7.1 were not found.
To resolve this, install the Developer Pack (SDK/Targeting Pack) for this framework version or
retarget your application. You can download .NET Framework Developer Packs at https://aka.ms/msbuild/developerpacks

[fail]: OmniSharp.MSBuild.ProjectManager
        Attempted to update project that is not loaded: c:\Users\richa\BrackeysTutorial\Assembly-CSharp.csproj

This result of this was that IntelliSense didn't work and I got various other errors in the log when I started typing. What is the best way to fix this problem?