I have not found a solution.
It should be in Settings > Notifications on Lock Screen
I have mine set to Show Content, but I turned off the Opera Max.
But, it still shows the Opera Max widget on the Lock Screen.
If I set the Notifications on Lock Screen to "Hide Content" then I see an "Android System Content Hidden" widget.
If I set the Notifications on Lock Screen to "Do Not Show Notifications" then, of course, it doesn't show any notifications. This, I don't want because I would like to see notifications for such things as emails, messages received etc.
I just don't want to see the Opera Max widget.