Asp.net – C# What is the purpose of [Serializable], entities can be serialized without this feature

What is the purpose of [Serializable], entities can be serialized without this feature.

public class NotSerializableModel
{
    public int Id { get; set; }
    public string? Name { get; set; }
    public DateTime CreateTime { get; set; }
}

[Serializable]
public class SerializableModel
{
    public int Id { get; set; }
    public string? Name { get; set; }
    public DateTime CreateTime { get; set; }
}

    [Fact]
    public async void SerializableTest()
    {
        var serModel = new SerializableModel()
        {
            Id = 1,
            Name = "Test",
            CreateTime = DateTime.Now,
        };
        var noSerModel = new NotSerializableModel()
        {
            Id = serModel.Id,
            Name = serModel.Name,
            CreateTime = serModel.CreateTime,
        };

        var serJson = System.Text.Json.JsonSerializer.Serialize(serModel);
        var noSerJson = System.Text.Json.JsonSerializer.Serialize(noSerModel);

        Assert.Equal(serJson, noSerJson);
        Console.WriteLine(serJson);
    }

When must I use this feature.
I can’t find any more instructions now, Google is saying, this means that you can serialize?