add custom css on all page exept of one

add this to end of functions.php

function mmk_enqueue_script(){
    if( !is_page(123) ){
    wp_enqueue_style('responsive-css', get_stylesheet_directory_uri() . '/custom.css', false);
    }
    }
    add_action( 'wp_enqueue_scripts', 'mmk_enqueue_script', 999);

create a custom.css inside your theme directory. this CSS file will be applied to all pages except the one you specified.

update “123” inside if condition with page id where you don’t want custom css.

The above code will enqueue additional css based on the condition. for more info
https://developer.wordpress.org/reference/functions/wp_enqueue_style/
https://developer.wordpress.org/reference/functions/is_page/