Nothingness is the “ultimate reality,” as it were, the very bottom line. Though in nonduality we speak of the Absolute, the Absolute is really just a word for utter emptiness.
Nothingness is what ajata points to. Ajata, in Sanskrit, means no creation, no origination. In other words, nothing has ever actually been created—including nothingness. All that appears to have been created is empty of reality. Being unreal, they have not actually ever been “created.”
Nothingness is without beginning or end. It is, as you said, 100% empty. There is no “time” there, no “space,” nor “cause” or “effect.” As such, it does not “exist”; its existence being moot, we cannot say it does “not exist.”
The answer to your question is that nothing does not “manifest” anything. Not anything has ever actually been manifested. The appearances appear to you. You are unreal: what you therefore see cannot be real (including the “seer”). An unreal dream is being dreamed by an unreal dreamer.
All of these appearances have a beginning and end; they disappear. Nothing is what “remains”: it is the only “reality.”