<field id="test" translate="label" type="multiselect" sortOrder="11" showInDefault="1" showInStore="1" showInWebsite="1">
 <label>Cms Page</label>
<source_model>NamespaceModuleModelTest</source_model>
</field>

public function toOptionArray()
    {
        $options = [
            [
                'label' => __('-- Please select --'),
                'value' => '',
            ],
            [
                'label' => __('Home Page '),
                'value' => 'cms_index_index',
            ],
            [
                'label' => __('404 Page'),
                'value' => 'cms_page_view',
            ],
            [
                'label' => __('Product'),
                'value' => 'catalog_product_view',
            ],
            [
                'label' => __('Category'),
                'value' => 'catalog_category_view',
            ],

        ];
        return $options;

<source_model>NamespaceModuleModelTest</source_model>

<source_model>MagentoCmsModelConfigSourcePage</source_model>