Hello Marco,
sorry, I was distracted by other daily topics. I used your guide and am currently running into an issue at the following step:
here I am trying to use your previously shared expression
{
"value": "@{items('Apply_to_each_2')}"
}
I used the same names in the apply to each parts, so references should be correct, however I got a note stating:

This translates to "The expression is not valid."
I am not sure why this is the case. If I used "dynamic content" I am able to select the "apply to each" value, if I only do enter your code manually to that level ("@{items("...")}") , that I try to add the dynamic content into the "..." spacer, it is no longer there.
I added the text now manually, although I am not quite sure if this works or not.

- Additionally ("Apply to each 2"):
When I tried the next step, I could not choose "varArray" as shown in your example on your website, it is only showing "varResponsesTemp" and "varResponsesDef". I checked your guidance and recognized that only "strings (Zeichenfolge in German)" are to be selected here, whereas arrays aren't.

So I changed the setting of "Initialize variable-varArray" from array to string and was able to select it here. Was the screenshot just outdated?
It wasn't particularly mentioned in your text, I just noticed the added function. So I changed the setup to match with yours by adding "Bereich" or "scope" to the flow, it eliminates the error message I receive for flow testing.
"Create item":
I could not select the varArray as dynamic content. So I went back to "Initialize variable-varArray", chose array instead of string, was able to add it in here and left the selection in "Append to array variable-varArray", it was at least not dismissed automatically.

Now, trying to save it, I get the following notice:

I expected that the JSON part was causing trouble, but I am also stuck with all above.
Please help me figure it out.