Hi there!
Glossary terms in Pressbooks need to be linked manually through the editor in each chapter. This chapter of the User Guide describes this process: https://guide.pressbooks.com/chapter/create-and-display-glossary-terms/. If you highlight a term in your chapter editor that corresponds to an existing glossary term and click the Glossary term icon in the visual editor, the existing term will be automatically proposed as an option to link.
An auto-linking option, like you might know from other platforms, like your LMS or a Wordpress site with such a plugin installed, is not available on Pressbooks.
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