how to process my array to be associative on first two levels and on third to have simple value

I'm trying to construct an array where there only strings and the array would look like this key->key->value

To explain it I attached two screenshots below.

I start with this:

After my code below I'm 90% there, yet there is an array in value on the third level instead of simple value.

Here is some code:

    $theme = ThemeHandler::with('sections.settings')->find($activeTheme);
    $themeSettings = $theme->sections;
    $themeSettings = collect($themeSettings->toArray());

    // dd($themeSettings);

    $themeSections = [];
    foreach ($themeSettings as $key => $value) {
        $settings = collect($value['settings']);
        $settings = $settings->mapToGroups(function ($item) {
            return [$item['key'] => $item['value']];
        });
        $themeSections[$value['key']] = $settings->toArray(); 
    }
    dd($themeSections);

I would like to end up with this structure

key->key->value

and not

key->key->single_element_array->value

I'm not sure how I end up with an array at the bottom level when I do this

return [$item['key'] => $item['value']];

inside the mapToGroups, which is a function found here: https://laravel.com/docs/5.8/collections#method-maptogroups

Maybe I misunderstand how mapToGroups work. Anybody has an idea how to get key->key->value structure output?

via Chebli Mohamed