We can posit that our "consciousness", as we experience it, resides entirely in our physical bodies, and that exact duplication of some subset of those bodies can create a consciousness exactly the same as ours. So any observer outside our body will be indifferent to whether they deal with the original or the copy.

But unless there is some communication between the two consciousnesses, you will experience the copy as something outside yourself. You won't have its memories after the moment of duplication, and you won't experience continuation. If your body dies, your consciousness dies. So while the world can have endless copies of you, and perhaps each copy feels like you, you still experience mortality. Your consciousness ends with the particular physical construct sustaining it.

At least, in the posited model.

The gholas of Dune are aware of this, and don't imagine themselves immortal though they know copies of themselves will be made after their departure.

They scan you, break you down, then transmit and create a new you. Now if you re-order this a little. Scan, transmit, create and then break down the original. There are two of you, then the original is killed. This shows that during the original process the first is scanned and killed, then a new person created. This is exactly how mind uploading would work in terms of continuity for the person being uploaded. (It's also why I would never ever use a teleporter.)

This is exactly what mind uploading is, they scan you and upload you. Creating a new you. Then you die and the other you lives on. This is very clearly shown if you scanned and activated the copy before the first person died. Are you trying to imply that you would suddenly, as a single entity, be experiencing two perspectives at once? Because that just wouldn't be possible.

It is technically immortality for your memories, but not the specific physical instance of you.

Or how is it different that going into sleep and waking up?

Anesthesia, then, or fainting. You cannot wake up from loud noises, and you have no consciousness.

One can also image a transfer process that is just like what naturally happens with regular body cells changing every 7 years or so.

E.g your brain is slowly, over a period of years, replaced cell by cell with new compatible neurons. One by one, your old neurons are replaced with the new, designed ones.

Those can read the state of the neuron they exchange AND exchange signals with your regular neurons, so before and after one is replaced, your brain is still functioning normally. No "power off" phase.

How about that?

However this is completely different from the concept of mind uploading where your brain is scanned and simulated separately.