How to remove parent style.css from the header

The file ‘style.css’ is integrated via function ‘twenty_twenty_one_scripts’ in the parent themes functions.php.

function twenty_twenty_one_scripts() {
    // Note, the is_IE global variable is defined by WordPress and is used
    // to detect if the current browser is internet explorer.

    global $is_IE, $wp_scripts;

    if ( $is_IE ) {
        // If IE 11 or below, use a flattened stylesheet with static values replacing CSS Variables.
        wp_enqueue_style( 'twenty-twenty-one-style', get_template_directory_uri() . '/assets/css/ie.css', array(), wp_get_theme()->get( 'Version' ) );
    } else {
        // If not IE, use the standard stylesheet.
        wp_enqueue_style( 'twenty-twenty-one-style', get_template_directory_uri() . '/style.css', array(), wp_get_theme()->get( 'Version' ) );
    }

    // RTL styles.
    wp_style_add_data( 'twenty-twenty-one-style', 'rtl', 'replace' );

    // Print styles.
    wp_enqueue_style( 'twenty-twenty-one-print-style', get_template_directory_uri() . '/assets/css/print.css', array(), wp_get_theme()->get( 'Version' ), 'print' );
...

To change this, disable function ‘twenty_twenty_one_scripts’ in the child themes function.php

function remove_my_action() {
    remove_action( 'wp_enqueue_scripts', 'twenty_twenty_one_scripts' );
}
add_action( 'wp_head', 'remove_my_action' );

Copy the Code of function ‘twenty_twenty_one_scripts’ into the child themes function.php, rename it and remove (or comment out) the first section of the function:

function my_twenty_twenty_one_scripts() {
    // Note, the is_IE global variable is defined by WordPress and is used
    // to detect if the current browser is internet explorer.

    global $is_IE, $wp_scripts;

    /*
    if ( $is_IE ) {
        // If IE 11 or below, use a flattened stylesheet with static values replacing CSS Variables.
        wp_enqueue_style( 'twenty-twenty-one-style', get_template_directory_uri() . '/assets/css/ie.css', array(), wp_get_theme()->get( 'Version' ) );
    } else {
        // If not IE, use the standard stylesheet.
        wp_enqueue_style( 'twenty-twenty-one-style', get_template_directory_uri() . '/style.css', array(), wp_get_theme()->get( 'Version' ) );
    }
    */

    // RTL styles.
    wp_style_add_data( 'twenty-twenty-one-style', 'rtl', 'replace' );

    // Print styles.
    wp_enqueue_style( 'twenty-twenty-one-print-style', get_template_directory_uri() . '/assets/css/print.css', array(), wp_get_theme()->get( 'Version' ), 'print' );
...

Activate the new function ‘my_twenty_twenty_one_scripts’ in child themes function.php

add_action( 'wp_enqueue_scripts', 'my_twenty_twenty_one_scripts' );