TYPO3 Core

Using a select type with renderTyp selectCheckBox in the sites configuration:

'myOptions' => [
    'label' => 'Options',
    'config' => [
        'type' => 'select',
        'renderType' => 'selectCheckBox',
        'items' => [
            ['Option A', 'option_a'],
            ['Option B', 'option_b'],
            ['Option C', 'option_c'],
            ['Option D', 'option_d'],
        ],
    ],
],

The options are stored in config.yaml as an array, e.g.:

myOptions:
  - option_a
  - option_b

But after saving the options are not activated in the form anymore. This is due the fact that for the renderTypes selectSingleBox, selectCheckBox and selectMultipleSideBySide the selected items are expected as a comma-separated list. So correct would be instead:

myOptions: 'option_a,option_b'