“Why does an all-perfect being create? If perfect, why?”

Spiritual traditions have various answers to that question.

My first question is whether perfect is an accurate description. I believe that etymologically speaking 'perfect' originally meant 'complete', thus whole, not necessarily perfect in the modern sense.

It then all depends upon which level of divinity you are talking about.

The Hindus have both Brahman and Brahma. Your response seems to be referring to Brahma, a complete oneness. Manifestation of the universe is called 'lila', which is often translated as divine play, which may or not be an accurate representation of what is going on. Metaphorically speaking, I prefer to see God as either an artist or scientist, trying to invent something, or create something beautiful, a great work of art.

There are other ideas in various philosophies, but in the end, we never can know for sure.