Hello.

The trigger should be a segment and not a list. So in the segment you should be like this - https://prnt.sc/5oHx5j5W-6mp. I can not think of any way to get the “update” event. The only you can do is to get them in the flow when they set a property that was not set before. And that is fine for what you need. You do not care if i change my name (that would be also weird).

So use a trigger flow when someone enters that segment and let me know how it went.

@StefanK 

The suggestion @Mail-Marketing gave is a great suggestion, the only problem there would be if you don’t collect Last name or if it is not a required field, or maybe you collect it somewhere else to apart from the preference page.

So the suggestion would be to have a preference page with a required field that you don’t collect anywhere else so when people update the preference page this field will be added to their profile. So the trigger would be similar to what @Mail-Marketing explained. Segment where that specific property is set but not necessarily last name, it can be something else.

Or you can use a segment something similar to this..