Airspace near stairs without windows and very dark

The whole thing is of course not optimal. All your suggestions have advantages and disadvantages. Is the provisional intermediate floor still going to be completely removed and is it currently only serving as a framework? If yes, I would simply remove the boards briefly and see how much light then comes from below.

Surely the podium will be removed. Then light will come from the door all the way up, and since it is painted white, it already looks quite different.
I would install a daylight lamp there, possibly with a motion detector.
A window is not only expensive and susceptible as a roof window, you have to clean it, and you have a hard time reaching it. I wouldn't put myself through that for a hallway.

We did not want to install a skylight, but rather a long window in the side exterior wall at the height of the upper floor. A skylight constantly gets dirty and is too difficult to clean.