Hi there,
Avery is using the Header Element on archive pages.
https://docs.generatepress.com/article/header-element-overview/
Which is replaces the standard entry header that would include the description.
Edit the Header Element and below the {{post_title}}
add:
{{custom_field.description}}
Alternatively you can delete that Header Element and the default Entry Header with Title and Description will be displayed – but it will be above just the content ( not the content + sidebar )