When getting notifications while not on the computer, they show up and removed after a few seconds, but I didn't see them.
They are then left in the notification list (super+v or click the clock).
The issue is that the top clock doesn't show any indication that there are missing notification.
Any idea how to show an indication that there pending/missed notifications?
See screenshots:
You can use the Notifications Alert GNOME shell extension. This is how the extension works:
The extension also lets you customise the rate of blinking, set up blacklist/whitelist etc.
Another less flashy alternative is provided by the Always Indicator extension. This is how this one works:
Refer to this to learn more about installing and configuring GNOME extensions: How do I install and manage GNOME Shell extensions?