hello @jakek can you clarify what you mean by Identify widget? Is this a widget in another Instant App template? Or another Esri web app? Or something new?
I just came here to ask the same. I would assume when you click on a line and the popup comes up? A feature you may not want to edit, just look at the data?
In Web Editor and the Instant App, you can access the popup through the Selection dialog, for any selected feature. We have not implemented a way to access the popup without selecting the feature, as we wanted to focus on editing interaction and pan.
We haven't received a lot of feedback to implement a "popup" or "identify" state to Web Editor or the Instant App but could consider it if we get more demand.