I had to add "using System.Web.Mvc;"
AND I had to run "Install-Package Microsoft.AspNet.Mvc" in the Package Manager Console.
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Further: this bit
// Requires using Microsoft.AspNetCore.Mvc.Rendering;
Should be higher up in the tutorial.
Just realized mine isn't very clear. The first comment was because I fixed that before moving on in the tutorial. After I moved on, I added the "using" statement that's commented out and it fixed the first problem. If you moved the comment about the using statement to above the first instance of "SelectList" it would be fixed.
Thanks to Brittany, I was able to find that
using Microsoft.AspNetCore.Mvc.Rendering;
was missing. Now SelectList is recognized.
That's all included in https://docs.microsoft.com/en-us/aspnet/core/fundamentals/metapackage-app
Most helpful comment
Further: this bit
// Requires using Microsoft.AspNetCore.Mvc.Rendering;
Should be higher up in the tutorial.