I've seen people online using the stamp tool in FL Studio to write scales. As far as I can tell, Logic Pro X does not come with this feature. Is there a plugin (has to be AU for my purposes) that simulates this feature and what is its name?
There's a versatile plugin called Scaler from Plugin Boutigue. It's available as an AU.
Also there is InstaScale by WA Production. This is more a scale learning and composition support plugin, available as AU as well.
Another composition support plugin helping with scales is MelodicFlow by feelyoursound. This is available as VST only.