You are quoting from the max mueller translation of the Taittariya Upanishad 2.6.1.
Shankara's bhashya of this verse explains it very clearly. As Brahman is sentient, it is capable of desire. However, this desire is not same as that ourselves.
Answer : No, since It is capable of desiring. It is not certainly a
matter of experience that one who can desire can be insentient. And we
have said that Brahman is, indeed omniscient ; and so it is but
reasonable that It should be capable of desiring.
Objection: Since Brahman has desires, It has wants like ourselves.
Answer : Not so, for It is independent. Such defects as desire cannot
impel Brahman to action, just as they do others, by subjecting them to
their influence. What then are these (desires of Brahman ) ? They are
by nature truth and knowledge, and they are pure by virtue of their
identity with Brahman. Brahman is not impelled to action by them.
But Brahman ordains them in accordance with the results of actions of
the creatures. Therefore, Brahman has independence with regard to
desires. So Brahman has no want. And this follows also from the fact
of Brahman’s nondependence on any other means. To explain, Brahman has
no dependence on accessories etc., as others have whose desires are
not identified with themselves but are dependent on such causes as
righteousness, and require the extraneous body and senses as their
Brahman, as reflected on Maya, is the material cause of the
world, and It is possessed of desires that are the modifications of Maya. However, Brahman is pure consciousness and is unsullied by Maya.
The one becoming many here does not refer to becoming something
extraneous as one does by begetting a son. How then ? Through the
manifestation of name and form that are latent in Itself When name and
form, existing latently in the Self, get manifested, they evolve
into all the states by retaining their intrinsic nature as the sell
and remaining indistinguishable from Brahman in time and space. Then
that evolution of name and form is (what is called) the appearance of
Brahman as many. In no other way can one justify either the evolution
of Brahman as a plurality
sah akamayata : sah, the Self from which space originated ; akamayata, desired.
How ? Bahu syam: syam, I shall become, bahu, many. This, Brahman says I will become many.
Brahman, srstva, having created; tat , that, this world. What did He do ? The answer is: tat eva into that very world - which had been created ; anupravisat, He entered.