The ValidationSummary component is named AspNetValidationSummary to avoid conflicts with the Blazor ValidationSummary component. This tag name will probably change in the future, to more closely align with the original ASP.NET ValidationSummary component.
Original Microsoft implementation of the ASP.NET ValidationSummary component is at: https://docs.microsoft.com/en-us/dotnet/api/system.web.ui.webcontrols.validationsummary?view=netframework-4.8