@kophaiem79
That fixed the extension. However, testing on Windows 11 23H2, clicking at https://www.example.com/ wasn't triggering a notification at all in Opera.
However, I noticed that Opera wasn't listed in "Settings -> System -> Notifications" in Windows, so I went to https://cleverpush.com/en/test-notifications/, clicked "Greetings", chose "allow" and clicked "Greetings" again to show a notification in Opera and that added Opera to the notification settings in Windows.
Then, I cleared notifications by clicking the clock in the Windows systray to bring up notifications and clicked "Clear".
Then, I tried your extension in Opera again and clicking on the https://www.example.com/ page starting working and showing the notification. Clicking "open" on the notification doesn't do anything though. I don't think the ButtonClicked event is firing for some reason in Opera, just like you said. According to https://help.opera.com/en/extensions/apis/, Opera does have some limitations on the notifications API, but nothing specific to the firing of the event.
I also deleted all entries from "HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Notifications\Settings" in the registry and restarted Opera. Even though Opera was no longer listed in the Windows notification settings, your notification popup was still showing up.
So, there's definitely some quirkyness going on there. But yes, I can confirm the event listener issue in Opera. Sounds like a bug to me.