I'm CiCi Nguyen, from Boost Commerce, the company behind Boost Product Filter and Search App.
About your question, Boost Product Filter and Search App allows merchants to filter out broad keywords to bring more relevant search results with a feature called Stop Words. This feature works on both collection pages and the search result pages.
I recommend you to give Boost Product Filter & Search App a try as we offer a 14-day free trial. If you find my answer helpful, please accept it as a solution.
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When retrieving products by collection you can't filter them. Yeah... frustrating...
If you want to filter products you'll have to query them directly (products endpoint) https://shopify.dev/api/storefront/reference/common-objects/queryroot#products-2021-10
If you're listing by collection, I suggest you to create a tag for each collection, tag every product of the collection with it and query the list of products filtering by that tag.