Hi lingers,

Please check the default route in the Program.cs file.

// Configuring Routes.
app.MapControllerRoute(
    name: "default",
    pattern: "{controller=UserDetail}/{action=Index}/{id?}");

Hi lingers,

Its difficult to address the exact issue causing the error.

But as per the error the Index page is not found in the UserDetail folder.

Or might be UserDetail controller doesn’t exist in your Controllers folder.

Please verify this.

For handling any error and get the error details, please refer below link.

https://learn.microsoft.com/en-us/aspnet/core/fundamentals/error-handling?view=aspnetcore-8.0#iexceptionhandler