Extension of dormer roof single-family house 1960, solid

What does the roof structure look like? [...] Is the ceiling above the ground floor made of concrete?

I do not expect the ceiling here to be made of concrete, typical for the year of construction and construction type, and in this particular case I also fear that the problem lies in the fact that the ceiling and roof construction are not separated.

I assume that it is a wooden ceiling. If the ceiling and roof structure are connected, that would mean that the roof could not be changed/renovated without also removing the ceiling (at least partially), do I understand that correctly? Aside from the fact that increasing the height by 1 meter would be difficult. As a result, the rooms on the first floor would actually remain too small, which would then lead us to consider an extension again. Nevertheless, the roof/ knee wall would not be insulated, so that would still need to be done. I am going in circles. There is no development plan here.

I assume it is a wooden ceiling. If the ceiling and roof structure are connected, that would mean that the roof could not be changed/renovated without also removing the ceiling (at least partially), am I understanding that correctly?

The general idea is correct - I suspect statically not separated elements. Your photo is relatively worthless without indicating what exactly is seen from where. Clarification is the be-all and end-all of any renovation project.

Apart from the fact that raising it by 1m would be difficult.

Well, "just" tricky fiddling.