StartupTaskBuilder.cs

public class StartupTaskBuilder
{
    public StartupTaskBuilder() => _tasks = new Queue<IStartupTask>();

    public StartupTaskBuilder Add(IStartupTask task)
    {
        QueueTask(task);

        return this;
    }

    public IStartupTaskSequencer Build() => new StartupTaskSequencer(_tasks);

    private void QueueTask(IStartupTask task) => _tasks.Enqueue(task);

    private readonly Queue<IStartupTask> _tasks;

    private class StartupTaskSequencer : IStartupTaskSequencer
    {
        public StartupTaskSequencer(Queue<IStartupTask> tasks) => _tasks = tasks;

        public async Task StartAsync()
        {
            foreach(var next in _tasks)
            {
                if (await next.CanRunAsync())
                {
                   await next.RunAsync();
                }
            }
        }

        private readonly Queue<IStartupTask> _tasks;
    }
}