How to change the url the core search form submits to?

Question

The action value for the core search form is /search/node.

How could I get it to go instead to a different url for a custom View?

Answer 1

if you don't want to do it with code you can use Custom Searchit gives you the possibility to configure it from configuration page:
For node search you can change it from admin/config/search/pages/manage/node_search

Answer 2

You can use hook_form_alter or hook_form_FORM_ID_alter to alter a form.

Core's search block form has a form id of search_block_form, so you could implement with hook_form_FORM_ID_alter() like:

use Drupal\Core\Form\FormStateInterface;

function mymodule_form_search_block_form_alter(&$form, FormStateInterface $form_state) {
  $form['#action'] = '/my-custom-path';
}