Who does not exist among beings, nor among existents generally; without impurities in the whole world, that one is called Brahman.

Bhūtā — existents, beings, what has been born. Bhūta also means spirit, ghost, but here refers to what has come to be.

The brāhmaṇa does not exist in any category of the existent. One is unfindable because there is no “there” where to search.