I've created the sitemap.xml from the search console and upload it on the shopify but all my pages and collections were indexed but the products not. ( Indexed : About Us, Contact Us, Tracking Order page, and collections name ; Not indexed : products themselves ). I've contacted the shopify support but they said that in back end all seems to be good and don't know what would be the issue. Have you ever had that problem or do you know what should I do ? Would SEO Manager App help me to index them ? I can't afford to pay for a SEO expert...
Without seeing your store it would be hard to give any feedback. How long has it been since you submitted the sitemap?
Google makes the call on what items to index or not. You can have 100 items in your sitemap and Google could choose to ignore them all. That's not a likely scenerio but important to know.