I understand now that I was reading code that was from before .NET 6 that included a Startup.cs file. It seems that program initialization is now commonly done in Program.cs with top-level statements, so there is no longer a Startup.cs file to reference, causing the error. I ended up following a different tutorial that had what I needed, which was this one: https://learn.microsoft.com/en-us/aspnet/core/data/ef-rp/intro?view=aspnetcore-9.0&tabs=visual-studio-code