$form['modes']['display_modes_custom'] = [
'#type' => 'checkboxes',
'#title' => $this->t('Use custom display settings for the following @display_context modes', ['@display_context' => $this->displayContext]),
$form['modes']['display_modes_custom'] = [
'#type' => 'checkboxes',
'#title' => $this->t('Use custom display settings for the following @display_context modes', ['@display_context' => $this->displayContext]),