Paul here, from the Guru team.
You are correct; currently the search function in the POS searches product titles and not variants. If it did, I can imagine a search for "Large" in a clothing store would be quite chaotic! :P Also, variants are listed under their parent product, so we wouldnt be able to display a variant result on its own.
Have a good one!
I was having this same issue, we sell a variety of books/cards that are grouped into one main item on our website/inventory system ("Student Chapbooks") but also each have a unique title.
When I search on an Android device through the Shopify POS app for a chapbook title ("Aliens Can Do Everything") it will pull up the grouped Student Chapbooks, at which point a clerk can select the right title and check out a customer.
But on the iOS app, this still doesn't happen.
It seems like you've implemented this (searching within variants and tags) for Android, but not iOS. Any chance it will migrate over?