Why does CanDeserialize always return false when deserialization succeeds? - xml-serialization

Question

I am attempting to deserialize an xml string into an object, nothing strange about that. Everything was fine until I upgraded my project to .Net5.
In the upgrade, I had to add a reference to the package Microsoft.XmlSerializer.Generator, and alter the project file to add the following:
<ItemGroup>
<DotNetCliToolReference Include="Microsoft.XmlSerializer.Generator" Version="1.0.0" />
</ItemGroup>
That allowed me to create the XmlSerializer (first error was just weird). Now, however, every call to CanDeserialize on the XmlReader return false if the class has the XmlRoot attribute. Now, I can deserialize the xml text. That does work. But why would CanDeserialize fail based on that condition?
Below is the class and the code I am using to test in a console app (.Net5).
[Serializable, XmlRoot("TestObj")]
//[Serializable]
public class TestObj
{
public int TestVal;
}
static void Main(string[] args)
{
var serializer = new XmlSerializer(typeof(TestObj));
//generated by doing a test serialization of the class
var teststr = "<TestObj xmlns:xsi=\"http://www.w3.org/2001/XMLSchema-instance\" xmlns:xsd=\"http://www.w3.org/2001/XMLSchema\"><TestVal>2</TestVal></TestObj>";
using (var str = new StringReader(teststr))
using (var reader = XmlReader.Create(str))
{
if (serializer.CanDeserialize(reader))
Console.WriteLine(((TestObj)serializer.Deserialize(reader)).TestVal);
else
{
Console.WriteLine("Value cannot be deserialized into the given Type");
//try it anyway
var o = (TestObj)serializer.Deserialize(reader);
Console.WriteLine(o.TestVal);
}
}
}
My workaround is just to eliminate the CanDeserialize call and wrap the deserialization in a try.. catch, but I'm still curious why this is happening.

Answer 1

Okay, comments on the question from #dbc did lead me to try something else. A couple of details I left of the original question because it didn't seem relevant (due to the testing involved) is that the class I am trying to deserialize in my non-test is in a .Net Standard 2.1 library. While the project doing the deserialization is .Net5.
In the end, I got this work. I had to reference the Microsoft.XmlSerializer.Generator package in my .Net Standard based library, but not reference it in the .Net5 project.
In short, leaving the package reference off the Standard project caused one error, and including it in both caused another.