When I click the share icon on any of the posts.
EDIT: oh, the irony. An admin message just popped up on my site saying:
[Admin Notice] One of your themes or plugins needs updating for compatibility with upcoming Discourse core changes. (id:discourse.modal-controllers) Identified theme: ‘redditish’.
But when I check for updates on that theme, it says, “Theme is up-to-date, last checked: just now”