SUMMARY
When first going to the "Update" section in discover, the footer of the update list features two buttons "Select All" and "Select None" that can be used to manipulate the selected updates, as well as a sum of the total size of the updates. After installing only some of the updates, when the list of updates is shown again, the buttons are not shown, instead the footer only shows a checkbox labeled "Restart automatically after update has completed".

STEPS TO REPRODUCE
1. Start discover and go to the "Updates" section.
2. Verify that more than one update is available.
3. Click "Select None" and then check one update to be installed and click "".
4. Wait for the update to finish.

OBSERVED RESULT
When the list of Updates shows again, the "Select All" and "Select None" buttons are missing.

EXPECTED RESULT
The option to unselect all updates should still be available.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.27.4
KDE Frameworks Version: 5.106.0
Qt Version: 5.15.8

ADDITIONAL INFORMATION
During the update process itself, the footer changes to show a checkbox labeled "Restart automatically after update has completed" - and this remains after the update process completes. The issue is probably that the footer is not being returned to the "list possible updates" mode after, as needed, after it was changed to the "during updates" mode.