closed caption

Yes. If you want to use the text-to-speech option and auto-generate the captions, click "Insert/Audio/Text-to-Speech."

That will auto-generate the closed captions. Then click the text-to-speech clip in the timeline and you will see the Audio Options menu appear.

That is where you can add the captions, either directly generated from the Text-to-Speech or from a source file.

Here's a link to the Storyline articles about it: https://articulate.com/support/article/Storyline-360-Supports-Section-508-Accessibility-Guidelines 

Good luck!