The share link is enabled by default for all content items that you uploaded directly to your Authory account (instead of importing from a URL).
This is so because if you display directly upload content items on your portfolio, we require a destination where a visitor of your portfolio can be forwarded if they click on the content item preview.
However, that does not mean that anybody can see your content. The share link contains a unique hash code that's impossible to guess, meaning the content item will only be accessible in two ways:
If you add it to your public portfolio
If you share the share link