Can customers scan a barcode to reorder in a Shopify app?

Yes. Pets Lounge scans a barcode straight from the search bar, so somebody re-ordering pet food points their phone at the bag rather than typing the name. It has been live since October 2023.

This suits any shop selling the same thing repeatedly — food, supplements, consumables, spare parts. It is the shortest route from "I have run out" to "it is ordered".