There's no quick toggle for that. You can submit an official feature request here: https://access.articulate.com/support/contact/feature-request. (Note that submitting a request doesn't guarantee that the feature will be added.)
You do have the option to use Dialog layers. Those automatically block everything on the base of the slide and the player. Here's more info: https://access.articulate.com/support/article/Storyline-360-Dialog-Layers. Of course, with those, you need to add a Hide Layer trigger to return to the base. But they do prevent someone from using the player Nav buttons while viewing the layer.
