Starting from Animate 2020, you can do this through the advancedLayersEnabled property from the timeline object. Like this:
var timeline = an.getDocumentDOM().getTimeline(); timeline.advancedLayersEnabled = false;
Do you have a link to the latest JSFL documentation, I only find old documentations..
The new documentation is still not available but the team is working on it and it should be available soon.
Please stay tuned!