Isavasyam idam sarvam

Sarvam the word covers all that is here.

Physical objects, the natural world, living beings and so on.

It also covers the subject I.

What is sarvam  is none other than ishvara.

Hence the upanisad says isAvasyam idam sarvam.

All that is here is ishvara.

Now this ishvara, has ishvaratvam, or sagunatvam.
He is the karana and karya both, and he is the manifestation.

The manifestation is mithya, which means the karana ishvara appears in various names and forms.

Ishvara is pure consciousness.

Who or what is pure consciousness.

Jivatma alone is pure consciousness. Sakshi chaitanyam, neither part product or property of material manifestation.

The satyam is this pure consciousness, that is the truth of ishvara.

With maya upadhi, pure consciousness alone is manifest as all that is here, isavasyam idam sarvam.

Consciousness manifests as space. Space as air. Air as Fire. Fire as Water. Water as Earth.
Then all of these undergo panchikarana.

The saguna brahman is mithya. Brahman is nirguna shuddha chaitanyam.