Recently I was working on a website built before dotnetcore was even a thing It was targeting an older version of the original .NET Framework.
I am slowly modernising it. Firstly I upgraded the nuget packages and re-targeted it to .NET Framework version 4.8.
Next, as the solution was split into many projects I was able to migrate many of these projects to be netstandard.
The idea is that all that is left is to think about upgrading the website to a Razor Pages aspnetcore project from the classic model view controller website.
While I was doing this a build script was failing.
The error was error MSB4236 The SDK Microsoft.NET.Sdk specified could not be found and is because the project now includes dotnetcore projects that need building.
After some googling the answer was to upgrade the
Microsoft Visual Studio 2019 Build Tools installed on that server.
.NET Core Build Tools and/or
Web development build tools and install
Once this was done the build worked.