Minifying CSS & JS in WP-Admin Dashboard

Hi,
I have spent a lot of time trying to minify CSS & JS on the back of WordPress with no joy.
Also, there are many plugin/theme styles and scripts there that I can’t get rid of, this code doesn’t seem to work:

function remove_cssjs_ver( $src ) {
if( strpos( $src, '?ver=' ) )
 $src = remove_query_arg( 'ver', $src );
return $src;
}
add_filter( 'style_loader_src', 'remove_cssjs_ver', 10, 2 );
add_filter( 'script_loader_src', 'remove_cssjs_ver', 10, 2 );

remove_action( 'wp_head', 'rsd_link' ) ;

remove_action('wp_head', 'print_emoji_detection_script', 7);
remove_action('wp_print_styles', 'print_emoji_styles');
remove_action( 'admin_print_scripts', 'print_emoji_detection_script' );
remove_action( 'admin_print_styles', 'print_emoji_styles' );

remove_action('wp_head', 'wp_shortlink_wp_head', 10, 0);

function disable_embed(){
wp_dequeue_script( 'wp-embed' );
}
add_action( 'wp_footer', 'disable_embed' );

add_filter('xmlrpc_enabled', '__return_false');

remove_action( 'wp_head', 'wp_generator' ) ;

remove_action( 'wp_head', 'wlwmanifest_link' ) ;

function deregister_qjuery() { 
 if ( !is_admin() ) {
 wp_deregister_script('jquery');
 }
} 
add_action('wp_enqueue_scripts', 'deregister_qjuery');

function disable_pingback( &$links ) {
 foreach ( $links as $l => $link )
 if ( 0 === strpos( $link, get_option( 'home' ) ) )
 unset($links[$l]);
}
add_action( 'pre_ping', 'disable_pingback' );

add_action( 'init', 'stop_heartbeat', 1 );
function stop_heartbeat() {
wp_deregister_script('heartbeat');
}

add_filter( 'wpcf7_load_js', '__return_false' );
add_filter( 'wpcf7_load_css', '__return_false' );

function speedupadmin() { 
 if ( !is_admin() ) {
  wp_deregister_style('wp-admin');
  wp_deregister_style('fvp-backend');
  wp_deregister_style('cwginstock_admin_css'); //Back In Stock Notifier
  wp_deregister_style('wpmtst-admin-global-style'); //Strong Testimonials
  wp_deregister_style('trustpilotSideLogoStylesheet'); //Trustilot
  wp_deregister_style('wc-aelia-foundation-classes-admin'); //Aelia
 // wp_deregister_style('storefront-plugin-install') //Storefront Installer
  wp_deregister_style('arconix-faq-admin'); //Acronix FAQ
 }
} 
add_action('admin_enqueue_scripts', 'speedupadmin');

if ( !is_admin() ) {
  remove_action('wp_enqueue_styles', 'wp_enqueue_styles');
}

remove_action( 'wp_head', 'print_emoji_detection_script', 7 ); 
remove_action( 'admin_print_scripts', 'print_emoji_detection_script' ); 
remove_action( 'wp_print_styles', 'print_emoji_styles' ); 
remove_action( 'admin_print_styles', 'print_emoji_styles' );

add_action( 'admin_enqueue_scripts', 'admin_enqueue_scripts' );