ADDITIONAL INFORMATION Alt+C select 'Checking for updates..' page. Possibly use Alt+U shortcut for both 'No Updates' and 'Checking for updates..' pages.
Currently Discover uses different shortcuts to show "Update" page depending on its status. While Discover checks for updates, alt+c shows the "Update" page. While updates are available, you need to press alt+u. However, alt+n does not show the update page whhen no update is available, you need to press alt+u. I think that the same shortcut (alt+u) should be required to show the update page regardless its status.
This is a Kirigami thing. Moving there.