I found this thread, as I was looking for the same solution. And I think I figured it out. 

When one is ready to share prototype:
1. Go to the top of the navigation, and find “Settings” wheel icon (click)

2. Under “General”, you may see a pill that states your prototype is “unpublished”

3. Before publishing, set your preferred settings, including things like “exclude from search engines”

4. (Optional) Link your preferred domain, like a private portfolio, if you want to directly host it. Otherwise, the default hosting is through Figma (thanks, Figma!) 

5. When you’re ready, hit “Publish”

6. If the system successfully published (takes 1-2 mins), you should see a notification that says: Published! Your app is live at eURL] - Copy to clipboard at the bottom of your screen.

Copy/paste the link to test in a web browser. Upon opening (hopefully) you should see your workable prototype without the Figma Make’s workspace UI.

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Pushing updates after publishing an app:

- Every time you make a change in the AI UI from the time you hit Publish, you’ll need to take an extra step to update your published prototype so that the changes push through to the prototype-only link. (I think it’s nice as you get to control what you’re figuring out in your version controls, and what parts you’re committing to go “live”.)
- You can also Unpublish if you want to pull the app down. To do this, go to your Settings wheel again. 

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Let me know the pros and cons to this way of doing things. It’s the one way I figured it out, but of course, I’m open to other ways.

As a Figma user for years, I had expected that other ways to share the prototype would have existed (like, for example, I open the “Play” (presentation) button, I can share a link, and that link would only share the presentation only. But clearly, for one reason or another, publishing is important for sharing the prototype. 

Happy making!