Limit Search to Product Pages only unless I’m on Blogpage or Blogposts

I don’t fully understand, but:

function lw_search_filter_pages ( $query ) {

    // ...

}

if ( is_front_page () || is_home () ) {} else {

    add_filter ( 'pre_get_posts', 'lw_search_filter_pages' );

}

Another:

function lw_search_filter_pages ( $query ) {

    // ...

}
                                   // https://yoursite.tld/blog
$uri = $_SERVER [ 'REQUEST_URI' ]; //             $uri = '/blog';

if ( $uri == '/blog' ) {} else {

    add_filter ( 'pre_get_posts', 'lw_search_filter_pages' );

}