Direction of laying parquet longitudinally or transversely to the light incidence in the living room

The hallway doesn't matter. The question is first whether everything should be laid in one piece, or (differently) with dividing edges or necessary expansion joints. Personally, I prefer it as much as possible without them. And in this case, both hallways must inevitably subordinate themselves to the living area. Depending on the length, width, and laying pattern of the specific package, this can work better or worse.

Lay it down and try it out, then decide how you like it

Exactly, that's the most pragmatic approach.

We have laid lengthwise to the light incidence!

I want to emphasize a hallway about 10 m long and about 1.50 m wide – in its length?

The hallway would be totally unimportant to me compared to the living area...

But apparently not for the OP when thinking about the direction. I would actually change the direction at the transition between kitchen and dining room. And also have a flush threshold installed. This is a subtle zoning and not a stubborn adherence to the scheme.

If I were you, I would lay out the long hallway crosswise and align the other rooms accordingly.

In a conversation with a friend who is a carpenter, he recommended "30°" to me. After he implemented it once for a client at their request, he would never do it differently again. I am still thinking about it, but will probably lay it out crosswise to the main incidence of light.

Horizontal. Fits better in all rooms. I find emphasizing proportions more important than light incidence, and the latter is also better horizontally in the living room.