I don't get it. It is perfectly valid to use immutability and the Type system to enforce those invariants in c#.

    abstract class User {
        public string Name { get; }
        abstract bool IsActive { get; }
        
        public User(string name) {
            this.Name = name;
        }
    }

    class ActiveUser : User {
        public ActiveUser(string name) : base(name) { }
        private ICollection<Subscription> _subscriptions = new List<Subscription>()
        public IEnumerable<Subscription> Subscriptions => _subscriptions;        

        IsActive => true;
        public DeletedUser Delete() => new DeletedUser(Name, DateTime.Now);
        public void AddSubscription(Subscription s) => Subscriptions.Add(subscription);

    }

    class DeletedUser : User {
    
        public DeletedUser(string name) : base(name) { }
        public DateTime DeletionDate {get;}
        IsActive => false;
    
        public DeletedUser(string name, DateTime deletionDate) : base(name) {
            this.DeletionDate = deletionDate;
        }

        public ActiveUser Reactivate() => new ActiveUser(Name);
    }