Disable wp_is_mobile()

wp_is_mobile() does not have any filters or ways to override. What you’ll need to do is build a wrapper of your own around wp_is_mobile() and use that in your code where you’ve used wp_is_mobile().

Something like the following prototype could work for you. Ultimately a better option over the URL parameter might be to use a cookie value that you set/clear based on the user selected preference. See the PHP documentation on setcookie() for more on cookies.

function my_is_mobile() {
    static $is_mobile;

    if (isset($is_mobile)) return $is_mobile;

    if (isset($_REQUEST['mobile']) && $_REQUEST['mobile'] == "no")) {
        $is_mobile = false;
        return $is_mobile;
    }

    $is_mobile = wp_is_mobile();
    return $is_mobile;
}