julien15000 wrote: But i didn't manage to do the step where i can purpose the 4 themes (or groups of questions).
Limesurvey isn't providing Skip, SkipBack or Loop functions like other survey packages.
The straight forward approach is
A) To let the proband choose in advance which parts choose. You would offer the five parts in a question and the proband has to choose at least one part.

If you really want to ask for additional questions group after the proband filled out one questions group you have to copy all questionsgroups four times to allow every proband to choose during the survey.
You might be able to shortcut the process if you fix the order of the questions groups.
Then you would only ask the proband "Do you want to answers Questiongroup topic" Yes / No?
If No, you skip the group and ask again for the next question group.
That would save you the duplication of every group.