Note: See the feature/project-capability branch for a possible solution to IntelliSense issues by using the <ProjectCapability> feature.
Sample application demonstrating design-time Razor Intellisense issues on a barebones ASP.NET MVC (non-Core) app using an SDK-style project on top of .NET Framework 4.8.
Just open it in Visual Studio and build, restore should be automatic. Alternatively, you can just stay in the command-line and execute dotnet build.
To run it, set up an IIS website pointing to the src\AspNetMvcOnSdk folder.
If you open the Views\Home\Index.cshtml file, you'll see red squiggles around the word MvcHtmlString and design-time errors appear in "Error list".
I get these errors (note both the C# and Razor have LangVersion explicitly configured to 7.3, the last officially supported version on .NET 4.8):
CS0246 The type or namespace name 'MvcHtmlString' could not be found (are you missing a using directive or an assembly reference?)
CS8370 Feature 'nullable reference types' is not available in C# 7.3. Please use language version 8.0 or greater.
CS0234 The type or namespace name 'AspNetCore' does not exist in the namespace 'Microsoft' (are you missing an assembly reference?)
CS0115 '_Views_Home_Index.ExecuteAsync()': no suitable method found to override
You can try setting a breakpoint in the Razor file and attach to the w3wp.exe process of the IIS app pool. You'll see that debugging in Razor works fine even though there are these design-time errors.
For more information, see this issue: dotnet/project-system#2670 (comment)
Looking for a solution to MvcBuildViews or web publishing? Check out the feature/advanced branch for an example on how to do these.