Adding code to child theme functions.php to override parent theme behaviour doesn’t work

I am trying to override some behaviour in a parent theme (Blackoot Lite) and used this StackOverflow question as a guide.

My goals are twofold—I want to unregister a default sidebar in the parent theme, plus I want to add a custom header widget area. Neither thing ends up happening. 😒

Below is my code, which I put into the child theme’s functions.php:

<?php

add_action( 'wp_enqueue_scripts', 'enqueue_parent_styles' );

function enqueue_parent_styles() {
   wp_enqueue_style( 'parent-style', get_template_directory_uri().'/style.css' );
}

function wpb_widgets_init() {

    register_sidebar( array(
        'name'          => 'Custom Header Widget Area',
        'id'            => 'custom-header-widget',
        'before_widget' => '<div class="chw-widget">',
        'after_widget'  => '</div>',
        'before_title'  => '<h2 class="chw-title">',
        'after_title'   => '</h2>',
    ) );

}
add_action( 'widgets_init', 'wpb_widgets_init' );

function blackoot_lite_unregister_sidebar() {
    unregister_sidebar('sidebar');
    unregister_sidebar('footer-sidebar');
}
add_action( 'after-setup-theme', 'blackoot_lite_unregister_sidebar' );

Any advice would be much appreciated.

You may find this useful to understand how to add a widget area in WP.