<PackageReference Include="Microsoft.Data.SqlClient" Version="7.0.1" />

Microsoft.Data.SqlClient.ManagedSni.ResolvedServerSpn

This is used to hold the ServerSpn for a given connection. Most connection types have a single format, although TCP connections may allow with and without a port. Depending on how the SPN is registered on the server, either one may be the correct name.
namespace Microsoft.Data.SqlClient.ManagedSni { internal readonly struct ResolvedServerSpn { public string Primary { get; } public string Secondary { get; } public ResolvedServerSpn(string primary, string secondary = null); } }