deactivating an active plugin using if page

Instead of deactivating the plugin completely (which would deactivate it everywhere on your site) look at the plugin’s code and determine what JS and CSS it is enqueuing. Then in your theme’s functions.php you can dequeue that plugin’s JS/CSS – but only on whatever pages you want to disable the plugin on.

So for example, for the plugin Authorizer, if you want to remove the CSS from two pages, “about” and “contact”:

add_action('wp_print_styles', 'wpse_317011_dequeue_authorizer');
function wpse_317011_dequeue_authorizer() {
    if(is_page('about') || is_page('contact')) {
        wp_dequeue_style('authorizer-public-css');
        wp_deregister_style('authorizer-public-css');
    }
}

Just replace authorizer-public-css with whatever CSS file you need to from your specific plugin. And dequeue JS as well, if that’s needed.

Other conditionals like is_singular() work here too in case it’s not just Pages you’re dealing with.