WordPress REST API V2: how to get list of all posts?

Out of the box and using the core available hooks and API, you can’t have more than 100 items per response on WordPress REST API for performance reasons. For the second part of the question, you may remove some fields from the response by using _fields parameter in your request as you can see in the examples of the handbook:

    // option a: using comma separated fields names.
    https://example.com/wp-json/wp/v2/posts/?_fields=author,id,excerpt,title,link

    // option b: using array syntax.
    https://example.com/wp-json//wp/v2/posts?_fields()=author&_fields()=id&_fields()=excerpt&_fields()=title&_fields()=link

And theoretically if you own the website, you could remove fields from the API response by using the rest_prepare_{$this->post_type} dynamic filter for the post(s) type(s) you want to change.

if(!function_exists('wpse_382314_post_filter_data')) :
    function wpse_382314_post_filter_data($response, $post) {
        $response->data('post_title') = '';
        $response->data('post_content') = '';
    }
}

add_filter('rest_prepare_post', 'wpse_382314_post_filter_data', 10, 3);