Woo doesn’t filter out products with hidden catalog visibility outside of main shop loop. This is important to remember when using the REST API for front end display or general search results. This code snippet will keep them from showing outside of the admin. Source: whoischris.com

remove-hidden-products-query.php

<?php
/**
 * https://whoischris.com/remove-catalog-visibility-hidden-products-in-woocommerce-from-search-wp-rest-api-results/
 */

add_action( 'pre_get_posts', 'hidden_search_query_fix' );
public function hidden_search_query_fix( $query = false ) {
	if ( ! is_admin() && isset( $query->query['post_type'] ) && $query->query['post_type'] === 'product' ) {
		$tax_query = $query->get( 'tax_query' );
		$tax_query[] = [
			'relation' => 'OR',
			[
				'taxonomy' => 'product_visibility',
				'field'    => 'name',
				'terms'    => 'exclude-from-catalog',
				'operator' => 'NOT IN',
			],
			[
				'taxonomy' => 'product_visibility',
				'field'    => 'name',
				'terms'    => 'exclude-from-catalog',
				'operator' => '!=',
			],
		];

		$query->set( 'tax_query', $tax_query );
	}
}

Very good, thanks :)
Save my time..

You need to remove public in line 2.
And [] in line 10.

Hello, Chris - any idea why it will not work on the Category display also? looks like they are still taken in the loop on those

Thanks, saved a lot of time with this function!
By the way I had to make some changes. When tax_query is empty API was throwing me an exception, I had to check whether 'tax_query' was string or array :

if (gettype($tax_query) === 'string') {
			$tax_query = [];
		}

I have no experience with PHP, maybe it is a better way to fix this.