Update (and correct) the existing System.Text.Json article on polymorphism:
https://docs.microsoft.com/dotnet/standard/serialization/system-text-json-polymorphism

For additional information and context, see https://gist.github.com/krwq/a24138195a47fc248039314e8708dc40