Core would show up there if there was an update. You can see it on my screenshot.
EDIT: It doesn’t show up on the supervisor addon page that doesn’t make sense. Addon page shows addons. It just used to be on that page because there was no where else to put it. Now there’s a place to put it. Addons themselves show when they have an update. The info page on core / supervisor also show that. They just don’t have a nice little highlight.