Did Brahman split into multiple souls?
The exact verse you are referring to is Chandogya VI.2.3. The division is only apparently so, and is only seen from the aspect of maya. Krishna says in Gita Chapter 13 verse 16 (Swami Nikhilananda translator):
It is indivisible, and yet It is, as it were, divided among beings. That Knowable Brahman is the Sustainer of all beings, and also their Devourer and Generator.
This is the crux of the Advaita of Sankaracharya. The division is only apparently so. To understand this better, read the section called 'Adhyasa or Superimposition' immediately after the Introduction here - https://www.wisdomlib.org/hinduism/book/brahma-sutras
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