[Shopify] How can I remove a searchBox in my Shopify theme using a custom hook?

You can remove the default InstantSearch searchBox widget on your theme using the afterISStartRemoveDefaultWidget(_, defaultWidgets) custom hook.

For example:
 

document.addEventListener('algolia.hooks.initialize', function() {
  algoliaShopify.hooks.registerHook('afterISStartRemoveDefaultWidget', function(defaultWidgets) {
    // Find 'ais.searchBox'
    const searchBoxWidget = defaultWidgets.find(
      widget => widget.$$widgetType === 'ais.searchBox'
    );
    return [searchBoxWidget];
  });
});