Settings > Custom Data > Products > Click on the Pin next to the metafield you want to Pin

Hey @KirkN Thanks so much for this information, it's been the first resolution i've seen online in my weeks of research. I've been back and forth with google support and shopify suppot and they both seem to just blame eachother for the issue and nobo...

You just need to pin the metafield definition or else it wont be visible when you select columns and scroll down.