not true, but you are missing the closing " in all your item definitions under the heading Geschosse and delete the [icon] part or replace it with a real icon name (see link above); so try this:
// Haus
Group gH "Heim"
// Geschosse
Group gUG "Untergeschoss" (gH)
Group gEG "Erdgeschoss" (gH)
Group gDG "Dachgeschoss" (gH)
//Räume
Group gBAZ "Bastelzimmer" (gUG)
Sorry, I had the closing " in my file (just forgot to write here) and I think I also had a real icon name in brackets < > (I just could not manage to post/write it here).
@dandil just saw that did not pick up on it above, make sure to always use the straight quotation marks ", not the slanted ones “ ”; a subtle difference for our eyes, but slanted ones will cause errors (and are typically introduced by copy/pasting; you had them in your first post for in the definition for Bastelzimmer.
@lipp_markus Thanks a lot, now I got it and it works as I wished to (I have first get used to all details). I had everything right first but then got distracted by “Visual Studio Code” and it’s colors…
When pasting any configuration from .things, .items, .sitemap, .rules files, or logs etc here, please be sure to use the “Code Fences”, as others have done (see lipp_markus’ post for a great example)
Using these options keeps all your formatting - spaces, the correct quotation marks (often the forum converts the “straight” quotes into “smart” quotes (the slanted ones) within normal text, but anything within the Code Fences aren’t touched. This is important for us to be able to see exactly what you are trying to do, and what might be wrong
Glad to hear, however, that you’re making some progress