Space Sync for Confluence provides space list page. You can list syncing spaces in your site with the page.
You can go to the page from Apps menu.
You can search spaces by name, and filter only spaces that is syncing.
The following labels are shown if sync settings match the condition.
The destination space is in an external site.
The destination space in the external site can mention users in your site.
The destination space removed the sync setting. So, the sync isn’t available.