How many lamps are in the 7-meter long hallway?

For the layperson, your contribution is not helpful either. Who can really imagine something under lumen or lux? The ceiling height usually does not make much of a difference now unless you have a clear height of 3.5 meters. Whether 2.5m or 2.7m is actually irrelevant. Even if I now write that 1 lux corresponds to an illumination from a candle that is about 1 meter away from a wall, that helps little in most cases... If one wants to know exactly and plans to design walls relatively dark, one has to go to the lighting planner, otherwise, a visit to prefabricated house parks helps to have a rough guideline. What I actually want to say: Whether you plan 3 or 5 spots on 7 meters now plays more of a role for the look or symmetry. The light sources make the difference, and at least I have tried and tinkered quite a lot with that.

Googling helps in most cases, but for that you need concrete clues – and 4000 K is really the least significant figure. If links were allowed here, I would have provided them, but you have to find examples yourself of how bright 100 lux are. Spoiler: You find plenty.

You also find plenty of help for the calculation, but either way you have to deal with the subject matter yourself – or pay someone to do it and trust that they do it well.

I can report that I was allowed to take a look at a neighbor's house with the same construction. He has the 2 standard light points that are provided. And no extra staircase lighting. Unfortunately, the visit was during the day, so it wasn’t completely dark anyway. The lighting was sufficient for him. I will plan to add another light point. That should be enough. Thank you for your answers. Some were too technical for me (after all, I am a layperson). Now it will stay as someone suggested: between 2 and 4 light points.

That's okay. You should just remember this thread when selecting the luminaires and possibly take a closer look at the specifications of the candidates. Luminous flux, beam angle, ...

Lighting is, in my opinion, always a matter of taste. One person prefers it brighter, another darker, and so on, which is why, in my opinion, a calculation formula is of little help.

Of course, it is always better if you can see "your" planning live, but that is quite an effort. However, if I know, for example, that 100 Lux is a good guideline for a hallway in a private house, then I can start with that and adjust afterward. If I start with 20 Lux out of ignorance and then am disappointed, I may have to completely replace the luminaires because I am basically operating in the wrong category.