Although Hopin does offer inbuilt closed captioning, you can also create captions for your Google Slides presentations. Keep in mind that this method works for live captioning only.
Before sharing your screen on Hopin, open your presentation on the Google Slides page. Click the arrow button next to the Present button and choose Presenter view.
On the Presenter View screen hover over the bottom of the page and click the Captions button. Start speaking and the captions will appear automatically. Be sure to speak clearly and at a normal speed.
Share your screen and your audience will be able to watch the presentation as well as the captions.
You can also check out the Google Slides captions help page for more settings and information.