If somebody is still trying to find a solution, thing that was a blocker for me was a Shopify Search & Discovery app. You HAVE to install it and then go in that app, filters settings and enable filters for specific metafields! Check docs on this link and make sure to check first section requirements.
Regarding unauthenticated_read_product_listings access scope, my Hydorgen storefront already had this permission, but for other storefronts you might have to enable it.