I want to add an option for the available inventory in the “Sort by” drop-down menu. The reason is that the option in the menu right now doesn’t allow what’s in stock to come out at the top and I can’t continue to do it manually.
Correct.
You can not, because there are a limited number of “sort by” options engineered into the Shopify COLLECTIONS array.
However… check out this post for some details on how I was able to handle “sort by inventory”
I was not satisfied by any of the answers in the community so I put this post together showing how to modify the template code to order by stock. I think this should be built into Shopify
This “human idea” seems like common sense: “Push out of stock items to the bottom”
However, after trying to make this happen I do indeed see why Shopify has ignored this… with enough community support we could help bring this feature to Shopify’s attention, and with the right DEV team on their end a good solution could be reached by enhancing the Shopify core code and collection array. (further details in link above)
Good luck.