Select field with API content shows only the last entry

The CMS Questions
1

Dear my beloved kirby support,

I have a structure field with content, which should be shown in a selcet field.

Like in the manuel:

Print_version:
    type: select
    when:
      print: true
    options:
      type: api
      url: "{{site.url}}/publication_collection.json"

Then I make a route in config:

'routes' => [
[
    'pattern' => 'publication_collection.json',
    'action' => function () {

        $pubsArray = [];
        foreach (page('offentlichkeitsarbeit/veroffentlichungen')->publications()->toStructure() as $pub) {
            $pubTitle = $pub->title();
           
            $pubsArray[$pubTitle->toString()] = $pubTitle;
        }
        return $pubsArray;
    },
]

],

When I check the JSON file, it shows an array with key/value pairs as expacted.

I used the same/very similar setup in a site (version 3.9.) and it worked perfectly but now:
The select field is showing just the last item in the list of the JSON. How and why?

–––––
I updated to 4.1.2.
The select field is wrapped in a structure in a block (not sure if that might be a problem here)

Has anything changed in kirby 4 in this matter?
Kind regards and thanks for looking into it.

2

Ok, I have it. It was the structure of the content, while I just needed the value, it gave me the title field… At least that is how I understand it. When you just take the value, then it work fine.

'routes' => [
[
    'pattern' => 'publication_collection.json',
    'action' => function () {

        $pubsArray = [];
        foreach (page('offentlichkeitsarbeit/veroffentlichungen')->publications()->toStructure() as $pub) {
            $pubTitle = $pub->title()->value;
           
            $pubsArray[$pubTitle] = $pubTitle;
        }
        return $pubsArray;
    },
]