With Google enabling mobile-first indexing for stores, they also include a little note about the structured data:
Your site may have structured data embedded on your desktop pages that can drive rich snippets in Google’s search results pages. If this structured data is absent on your mobile site, you could lose those rich snippets and the click-through rate (CTR) benefits they convey
It’s a nice reminder to make sure your store is serving up the same structured data to mobile customers as desktop customers.
A lot of sites in the past had desktop and mobile split so the mobile sites were devoid of them. Even now, some AMP sites (which are just specialized mobile sites) don’t have the correct structured data or are missing it entirely.
Shopify has been pushing responsive themes for awhile which helps with this quite a bit. With a responsive theme, the same version of the theme is used for both mobile and desktop visitors. It just looks and is organized differently on mobile (e.g. shrunk navigation, larger fonts).
That means if you have structured data working already, mobile-first indexing shouldn’t change anything. In fact, it might be an improvement because the mobile search results have a lot more hidden search enhancements that structured data seems to help but aren’t documented officially.
If you’re using JSON-LD for SEO, your store is probably going to be fine. The app doesn’t care about mobile or desktop browsers and does the same thing for both.
If you’re using another app (why? 🙂 ) or relying on your theme (you shouldn’t 🙂 ) then you might need to double check. In theory all apps and themes should be fine but it’s best to not assume these things. The stories I could tell… but I won’t.
In summary, mobile-first indexing is a great thing for structured data though you might need to check on a few things to make sure all of your sources are compatible.
And if you’re not using JSON-LD for SEO yet, you’re missing out on an easy SEO win.