尝试删除 .csproj 文件中的 Microsoft.AspNetCore.Razor.Design .那对我来说很完美.当我将项目从 .NET Core 2.2 迁移到 .NET Core 3.0 时，我遇到了同样的问题.

Try deleting Microsoft.AspNetCore.Razor.Design in your .csproj file. That worked perfectly for me. I had the same issue, when I migrated my project from .NET Core 2.2 to .NET Core 3.0.