You can now use two new tasks in Shopify Flow.
Trigger - Product variant back in stock
When a product variant goes from 0 or less to 1 or more, you can now trigger a workflow to run. For example, you might want to always publish a product when one of its variants is back in stock.
Trigger - Product variant out of stock
When a product variant goes from 1 or more to 0 or less, you can now trigger a workflow to run. For example, you might want to send an email or Slack message when a variant is out of stock.
Flow also provides an Inventory quantity changed trigger, which also works at the variant level. Going forward, for use cases where the location does not matter and where you simply care about in-stock or out-of-stock, these new triggers should be used, as they are much simpler.
If you need to do inventory based on locations, or if you want to track low stock, then you should continue to use the Inventory quantity changed trigger.