Thank you Paul. I misunderstood this change. From reading more about the Squarespace app and use with Square card readers, it seems the app is really only appropriate for pop-up type situations, since there is no option to use Square Register or Terminal.
From what I gather, the other option people have is to use Shopify Lite with Shopify POS if they need a more robust POS/ inventory system, but like the Squarespace website tools better. It seems one can pop Shopify Lite items into a Squarespace store. I imagine once a store gets beyond 30 or so items, though, that solution becomes a pain to manage.