OwDafuq

var persons = new[]
{
    new Person{ Id = 1, FirstName = "A", LastName = "A", Age = 20 },
    new Person{ Id = 2, FirstName = "A", LastName = "B", Age = 20 },
    new Person{ Id = 3, FirstName = "A", LastName = "C", Age = 30 },
    new Person{ Id = 4, FirstName = "A", LastName = "D", Age = 30 },
    new Person{ Id = 5, FirstName = "B", LastName = "A", Age = 10 },
    new Person{ Id = 6, FirstName = "B", LastName = "B", Age = 20 },
    new Person{ Id = 7, FirstName = "B", LastName = "C", Age = 10 },
};

var result = persons.GroupBy(x => new { x.FirstName, x.Age }).Select(x => x.First());

foreach (var element in result)
{
    Console.WriteLine(element);
}

class Person
{
    public int Id { get; set; }
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public int Age { get; set; }

    public override string ToString() => $"{Id}, {FirstName}, {LastName}, {Age}";
}

internal static class RuleExtensions
{
    public static IRuleBuilderOptions<T, int> ValidateId<T>(this IRuleBuilder<T, int> builder)
        where T : IHasId
    {
        return builder.Must((t, x) => t.Id > 5);
    }
}

class FirstTestValidator : AbstractValidator<FirstTest>
{
    public FirstTestValidator()
    {
        RuleFor(x => x.Id).ValidateId().DependentRules(() =>
        {
            RuleFor(x => x.Guid).NotEmpty();
        });
    }
}

private ServerGroup selectedGroup;
public ServerGroup SelectedGroup
{
	get => selectedGroup;
	set
	{
		selectedGroup = value;
		loadProcesses();
	}
}
public ObservableCollection<ServerGroup> Groups { get; }
public ObservableCollection<Process> Processes { get; }

private async void loadProcesses()
{
	Processes.Clear();
	//get response from API, etc.
	var response = new List<Process>(); //example

	response.ForEach(Processes.Add);
}

<ComboBox SelectedItem="{Binding SelectedGroup}" ItemsSource="{Binding Groups}"/>
<ComboBox SelectedItem="{Binding ......}" ItemsSource="{Binding Processes}"/>

"WriteTo": [
  {
    "Name": "Console"
  },
  {
    "Name": "Seq",
    "Args": {
      "serverUrl": "http://localhost:5341/",
      "apiKey": "key",
      "restrictedToMinimumLevel": "Warning"
    }
  }
]