Hmm, I think that most people in this forum have a day job and reply and/or comment on an issue when they have time to do so. e.g. nobody replied to my post I created 3 days ago. While it easy to reply to a simple and clearly defined question, it might be not so easy for a question that does not even state the version of the release.

I'm not sure what you are reading but it for me it says:

macOS : >= 10.8 or Growl if earlier.

This means that you need Growl for macOS releases earlier than macOS 10.8.

Yea, I got that. I was talking about the macOS version as well. The test I ran was on macOS.

You do not add applications to the Notification Center. Never have, never will.
As soon as an application uses the macOS API to send a notification, an entry is created in the Notification Center for that application.

Joplin is a react-native application and uses Electron on macOS. Notifications are handled by the module you referenced, so really this module is sending the notifications. This is the reason why the entry you are looking for in the Notification Center is terminal-notifier.

This is ok, but you could have at least mentioned the version of Joplin you are having the problem with or the version of your OS. A problem report that only says it does not work is impossible to work on. You must admit that a bit more information is needed.
As mentioned before, it works for me, so most likely it works also for other people, so your problem might have to do with your setup. Maybe nobody replied, because they don't have that problem.

In any case, more info is needed, since we have to determine what the culprit is.

A debug log always helps, because we can see, if there's an error in Joplin or at least we can narrow down the problem.
So I suggest to set an alarm for time X and we can check what the log says at time X.
Additionally, maybe there's an entry in the macOS system log. You can open the macOS Console application and look for any entries at time X. Other than that, I currently do not have any other ideas.

Just to be clear, I'm a user of Joplin, like you. I am not the developer.

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