This is a follow-up to Update manager never popping up which happened to be mistitled after a bit of investigation).
The new behaviour of update-notifier out-of-the-box in Ubuntu 26.04, configured with com.ubuntu.update-notifier show-updates-status-icon false, is to hide both its tray icon and its notifications (regardless of time conditions and other configurations, since as coded no tray icon entails hiding the notification).
I think this default behaviour must be changed since :
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Users using will never be notified of any regular update
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Users opting out of unattended-upgrades will never be notified of any update of any kind, security included
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Users wanting to be periodically notified of standard updates (e.g. every 7 days) have no way to to do it without enabling a tray icon showing immediately when updates are available.
What could be done, I think is
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to enable notifications to be sent even when the tray icon is hidden
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and rely on the existing parameter (
com.ubuntu.update-notifier no-show-notifications) to hide notifications if unwanted.