For variants and maybe products using Shopify fulfiller if "Track inventory" is not checked in the Shopify Admin calls to Mutations.inventoryActivate wrongfully succeed. The quantity set here will never be used. This call is a noop AKA a bug!
Furthermore, there is no way workaround this by checking that inventory is/is not tracked. Inventory Item tracked does not reflect the "Track inventory" checkbox.
Variant inventory_policy cannot be used to determine this.