settingsChangedInMemory
    .Subscribe(async _ => {
        var settings = Extract();
        await SaveSettings(settings);
    });

settingsChangedOnDisk
    .Subscribe(async _ => {
        var settings = await ReadSettings(settings);
        Apply(settings);
    });

settingsChangedInMemory
    .SelectMany(async _ => await SaveSettings(Extract()))
    .Subscribe(x => Apply(x));

await observable
    .ForEachAsync(async x =>
    {
        Console.WriteLine(x);
        await Task.Delay(1000);
    });