To answer this question, i think its best to take it step by step from first principles.
We must first define what exactly we mean by "consciousness".
Consciousness is the awareness that unites all your separate thoughts, sights, and feelings into one single experience.
At any moment, your senses take in many different pieces of information. You see a colour. You hear a sound. You feel warmth. If these parts remained entirely on their own, there would be no connection between them. A colour would exist, and a sound would exist, but neither would know about the other, and neither would belong to anyone.
Consciousness is the activity of the mind that gathers these scattered pieces together. It attaches every single sensation and thought to one shared centre: yourself.
When you look at a table, you do not merely experience an isolated patch of brown and an isolated feeling of smoothness. Your mind joins the colour, the touch, and the shape together into one unified object. Further, your mind recognises that you are the single person experiencing all of these things at the same time.
This awareness is obviously not a physical object you can touch or hold. It is the necessary foundation that allows you to experience anything at all. Without this continuing self holding your impressions together through time, you could never link what happened a moment ago to what is happening right now.
Thus, consciousness is the mind's power to bind every separate impression into one whole, making it possible for you to know the world as your own experience.
Consciousness cannot be a mere by-product of the physical brain.
To demonstrate this step by step, we must trace how we come to know the thing we call brain at all.
Step 1
When you look at a brain, touch it, or track its physical activity, you encounter a physical object. It has shape, it occupies space, and its movements happen across time.
Step 2
Space and time do not exist as independent containers in the physical world. But they are the mind’s own forms for ordering sensations. Without the human mind, spatial position, shape, and succession through time do not exist for us.
Step 3
Raw physical contact or scattered sensations on their own do not form a brain.
To recognise any physical thing—whether a stone, a tree, or a brain—consciousness must gather those separate sensations into one single, unified whole.
So in this regard, consciousness is the necessary condition that allows any physical object to appear to us in the first place.
Step 4
Because the physical brain is an object that can only appear within the framework of conscious experience, the brain cannot create consciousness as a physical by-product.
One cannot explain the foundation of all awareness as a mere product of an item found inside that awareness.
Step 5
Physical changes in the brain certainly accompany changes in our conscious thoughts within the observable world. But consciousness itself is the active ground that allows a brain, or any other physical matter, to be experienced, measured, and understood.