WPSOLR will replace the default query for archives, like search, taxonomy, author, ….
In your case, it will replace the 1 million products WooCommerce shop page, product search page, and product category page queries.
After a query is called on Solr, Elasticsearch, Algolia, or OpensSearch, WPSOLR sends results back to your theme’s standard WP loop to let it display the results as usual.
Other queries, like all queries called to build the product detail page, are not replaced.