poppers Yes I know this explanation, but if this Self is the only thing that exists then we still can say there's no individuality at all. There's no John_Mann "True Self" and one popper's "True Self" because it's just one thing.
Plato and Kant said that every object have a "true self" in an ideal realm (Plato) and these ideal "objects" are the only things-in-itself (Kant).
But Schopenhauer gone further and said if the real existence is beyond categories (time, space, etc) so there's no sense to keep the individualization among ideal objects. In this ideal realm must exist just one thing that he called "Will to Live" (Shunyata, Brahman...), a kind of blind force/energy that (for some unknown reason) needs to manifest itself in an objective world with the illusion of multi-individualization (Vishnu becoming infinite beings [Vishvarupa] in Baghavad Gita).
In Physics we have a similar concept called quantum vacuum fluctuation, a kind of "pregnant void", an empty state that can give origin to an entire universe.
Even in this sense, there's no self or Self.