How to deserialize array in the xml to different object types without type attribute?

We can manually add a type attribute to the xml token stream when parsing.

If you really really want to use deserialization, then I can suggest the following code.

Set of classes:

public class Profile
{
    public List<ProfileSection> ProfileSections { get; set; }
}

[XmlInclude(typeof(DefaultProfileSection))]
[XmlInclude(typeof(AddressProfileSection))]
public class ProfileSection
{
    [XmlAttribute]
    public string Name { get; set; }
}

public class DefaultProfileSection : ProfileSection
{
    public string Email { get; set; }
    public string Password { get; set; }
}

public class AddressProfileSection : ProfileSection
{
    public string Street { get; set; }
}

A custom xml reader that will add the necessary information on the fly:

public class TypeAddingXmlReader : XmlTextReader
{
    public TypeAddingXmlReader(string url) : base(url) { }

    // Define the remaining constructors here

    public override string? GetAttribute(string localName, string? namespaceURI)
    {
        if (base.LocalName == "ProfileSection" &&
            localName == "type" &&
            namespaceURI == "http://www.w3.org/2001/XMLSchema-instance")
        {
            var name = base.GetAttribute("Name");

            return name switch
            {
                "Default" => nameof(DefaultProfileSection),
                "Address" => nameof(AddressProfileSection)
                // add other class names here
            };
        }

        return base.GetAttribute(localName, namespaceURI);
    }
}

Use:

var ser = new XmlSerializer(typeof(Profile));

using var reader = new TypeAddingXmlReader("test.xml");

var profile = (Profile)ser.Deserialize(reader);

foreach (var ps in profile.ProfileSections)
    Console.WriteLine(ps.Name + " " + ps.GetType());

Namespaces:

using System.Xml;
using System.Xml.Serialization;

Note: but I would use linq to xml and not sweat it.