Buddhism which was dominant among the elites and aristocrats by 8th century was largely displaced out of India via scholarly debates.
This idea that east doesn’t believe in self is hokum
In Western Philosophy they are synonymous with "Self-Identity/Ego" etc.
In Hindu philosophy, the basic idea of "Self" comes from the "Samkhya System" (see https://en.wikipedia.org/wiki/Samkhya) which is what is followed by/built upon by other schools of Hindu Philosophy. In this model, "Self" aka "Purusha" is immutable and untainted/undifferentiated pure Consciousness. In Advaita it is known as "Atman". It is "Prakriti", the other aspect of reality which is mutable, that gives rise to "Buddhi"(Intelligence), "Ahamkara"(Self-Identity/Ego) and "Manas"(Mind).
You can see now how confusion arises when people use the same English word "Self" to describe different things in different contexts.