Personal Message Box for Individual Members

add_action( 'edit_user_profile', function ( $user ) {
    if ( ! current_user_can( 'edit_users' ) ) {
        return;
    }

    wp_nonce_field( 'wpide_member_message_' . $user->ID, 'wpide_member_message_nonce' );
    printf(
        '<h2>Personal message</h2><table class="form-table" role="presentation"><tr><th scope="row"><label for="wpide-member-message">Message for this user</label></th><td><textarea id="wpide-member-message" name="wpide_member_message" rows="4" class="large-text">%s</textarea><p class="description">Shown only to this user. Leave empty to remove.</p></td></tr></table>',
        esc_textarea( get_user_meta( $user->ID, 'wpide_member_message', true ) )
    );
} );

add_action( 'edit_user_profile_update', function ( $user_id ) {
    if ( ! isset( $_POST['wpide_member_message_nonce'] ) || ! wp_verify_nonce( sanitize_key( $_POST['wpide_member_message_nonce'] ), 'wpide_member_message_' . $user_id ) || ! current_user_can( 'edit_users' ) ) {
        return;
    }

    $message = isset( $_POST['wpide_member_message'] ) ? wp_kses_post( wp_unslash( $_POST['wpide_member_message'] ) ) : '';

    if ( '' === trim( $message ) ) {
        delete_user_meta( $user_id, 'wpide_member_message' );
    } else {
        update_user_meta( $user_id, 'wpide_member_message', $message );
    }
} );

add_shortcode( 'wpide_my_message', function () {
    $message = is_user_logged_in() ? get_user_meta( get_current_user_id(), 'wpide_member_message', true ) : '';

    return $message ? '<div class="wpide-my-message" role="note">' . wpautop( wp_kses_post( $message ) ) . '</div>' : '';
} );

add_action( 'admin_notices', function () {
    global $pagenow;

    $message = in_array( $pagenow, array( 'index.php', 'profile.php' ), true ) ? get_user_meta( get_current_user_id(), 'wpide_member_message', true ) : '';

    if ( $message ) {
        echo '<div class="notice notice-info">' . wpautop( wp_kses_post( $message ) ) . '</div>';
    }
} );