I’m sorry to revive a resolved thread, but I’m doing it for a good 
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We’ve added a neat generator of Shopify Flow variables to our app, Metafields Guru. This generator supports all Online Store 2.0 metafields, including the recently introduced “list” metafields. You can configure a metafield template in our app and then easily copy all the settings to a custom Shopify Flow action:
Hopefully, it will come in handy for our community while waiting for Shopify to release native support for OS 2.0 metafields!