I'm actually searching for the same thing. I (as a moderator) want to send short custom notifications to certain members in order to recommend them to engage in certain discussions/threads. I could of course do that within a private discussion (byobu), but I like the idea of giving a short memo-like hint via a notification which won't need a reply or any ongoing communication. It should just be used to draw attention to discussions which I want to recommend to individual members.
Have you found a solution for this, Eren65465024 ?
Is anyone aware of such functionality within an existing extension?