How to find if there entity with same type and with same entities in collection?

public class Conversation
{
    public Conversation(ICollection<Message> messages, ICollection<User> participants, ConversationType type)
    {
        Messages = messages;
        Participants = participants;
        Type = type;
    }

    public Conversation()
    {
    }
    
    public long Id { get; set; }

    public ICollection<Message> Messages { get; set; }
    
    public ICollection<User> Participants { get; set; }
    
    public ConversationType Type { get; set; }
}

public enum ConversationType
{
    Dialogue = 1,
    Conversation = 2
}

public class Conversation
{
    public Conversation(ICollection<Message> messages, ICollection<User> participants, ConversationType type)
    {
        Messages = messages;
        Participants = participants;
        Type = type;
    }

    public Conversation()
    {
    }
    
    public long Id { get; set; }

    public ICollection<Message> Messages { get; set; }
    
    public ICollection<User> Participants { get; set; }
    
    public ConversationType Type { get; set; }
}

public enum ConversationType
{
    Dialogue = 1,
    Conversation = 2
}

public class User
{
    public User(string nickname, string passwordHash, ICollection<Conversation> conversations)
    {
        Nickname = nickname;
        PasswordHash = passwordHash;
        Conversations = conversations;
    }
    
    public User()
    {
        
    }
    
    public long Id { get; set; }
    
    public string Nickname { get; set; }
    
    public string PasswordHash { get; set; }

    public ICollection<Conversation> Conversations { get; set; }
}

public class User
{
    public User(string nickname, string passwordHash, ICollection<Conversation> conversations)
    {
        Nickname = nickname;
        PasswordHash = passwordHash;
        Conversations = conversations;
    }
    
    public User()
    {
        
    }
    
    public long Id { get; set; }
    
    public string Nickname { get; set; }
    
    public string PasswordHash { get; set; }

    public ICollection<Conversation> Conversations { get; set; }
}