Check the Projects tab in the Edit → Addon Manager. If none of the Project checkboxes are selected, that is the message that would appear in the in the Addons tab.
Select at least the default 1st row checkbox and click the Refresh button.
(Also of interest but not related to your issue: To turn off default filtering entirely, changed from “Everyone” to “All audiences” and from “stable” to “All statuses”)
If no addons are listed after verifying the Projects and Filters are set correctly, there might have been a problem when generating the Addonlist-xx.json file generated after updating the collection on GitHub.