How do I add hreflang tags to Shopify?

Generally, Hreflang tags and meta tags are automatically created for every international domain you set up. However, for this to be useful on Shopify, you must have the same collections, products, pages, blogs, blog tags, and articles in each store. This is why most experts say that standard hreflang tags in Shopify are bad for SEO. I will advise you to search for solutions in the Shopify app store. I think an app like Multi-Store Hreflang Tags may provide a solution for you. It also has a very good rating on the app store.