Slide Layer: 1. trigger not working and 2. Screen reader is reading a hidden object

For me the slide does not move until I press play.

You should switch on the play/pause and the seekbar.

For number 2 I am confused. I suspect the reason is that you have a selected state so it is not switching to visited.

I would just set the layer to prevent user clicking on the base layer and then set the previous slide button you have to hide the object and remove the cover layer