Create Drop Shipments from Sales Orders against vendor selected for the lookup custom field

Settings > Preferences > Sales Orders > Field Customization > New Custom Field

Create a Loop-up data type custom field with "Vendor" module as related entity

Settings > Automations > Custom Functions > New Custom Function

Module: Sales Order

Copy and paste the Dropshipment for SO script.

Create connection for Zoho Inventory - zom

Settings > Automations > Workflow Rules > New Workflow Rule

Module : Sales Order

Workflow Type : Event Based

When an Sales Order is: Created / Edited

Filter the triggers: When vendor lookup field is not empty

Choose the appropriate custom function in the Action.

Save the workflow. On each salesorder creation / edit action, the workflow automatically creates a Drop Shipment Purchase Order