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  • okay. that was easy! here we go. simply adjust it to your needs:
    1. create a new entry in wp_options: “is_winner”
    2. insert that code to your functions.php:

    // register the meta box
    add_action( 'add_meta_boxes', 'my_custom_field_checkboxes' );
    function my_custom_field_checkboxes() {
            'winner_box',          // this is HTML id of the box on edit screen
            'Winner',    // title of the box
            'my_customfield_box_content',   // function to be called to display the checkboxes, see the function below
            'product',        // on which edit screen the box should appear
            'side',      // part of page where the box should appear
            'default'      // priority of the box
    // display the metabox
    function my_customfield_box_content( $post_id ) {
        wp_nonce_field( 'wp_nonce_check', 'myplugin_nonce' );
        echo '<label><input type="checkbox" name="is_winner" value="1" /> Winner';
        if(get_the_id() == get_option("is_winner")) echo " (currently selected)";
        echo "</label>";
    // save data from checkboxes
    add_action( 'save_post', 'my_custom_field_data' );
    function my_custom_field_data() {
        // check if this isn't an auto save
        if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE )
        // security check
        if ( ! isset( $_POST['myplugin_nonce'] ) || !wp_verify_nonce( $_POST['myplugin_nonce'], 'wp_nonce_check' ) )
        if ( isset( $_POST['is_winner'] ) )
        	update_option("is_winner", get_the_id());

    now in every post is a meta box along with ACF fields. when you check that meta box, the id is saved to the field in wp_options. this way, you save a lot of performance because there is no wp_query and you do not need to alter all posts!!