Do you get any details on the error? Could have been a glitch at the time Google was trying to fetch the xml?
Google sometimes keeps status as "couldn't fetch" even if it's still pending to read the XML. observe for few more days and try to resubmit the sitemap.
You can as well post the issue in the Google Webmasters community forum.
Hope this was helpful
We are also facing problem with the sitemap whenever we are trying to access the whole sitemap of the website, please check screen shot - https://prnt.sc/106yofg
This website is heavy in products, when we are trying to access individual sitemaps for the collection, pages and blog, these are working fine but we are not able to access product based sitemap from our side as we do not know the assigned starting and end ID of the product on Shopify store.
Please help us if anyone knows the solution for this problem.
Thanks in Advance!!!
Tracking visitors/clicks/queries to your product pages is highly important because they are the money pages.
I wager that you're using URL Prefix option, instead of Domain option when submitting your domain.
Usually, you’ll want to go with domain to ensure that every single one of your pages is indexed by Google. However, if you already use Domain option but your GSC still could not fetch product pages sitemap, try resubmitting your sitemap file.