Ok, thank you for that!
I set up the Facet for Nachname Contains a Space with a custom text filter.
Now that I have isolated the names that I want, those that I can be sure are full names that should be in Weitere Zugehörige Personen, and I filtered for blank cells for Weitere Zugehörige Personen.
I have tried to copy it with
if(
and(not(W Weitere_Zugehörige_Personen.trim()), not(Nachname.trim() == "")),
Nachname.trim(),
Weitere_Zugehörige_Personen.trim() + ", " + Nachname.trim()
)
Keeping in mind what you said about Boolean operators.
I found this, but it did not really solve the problem.