How to get Shipment item collection by shipment item id Magento 2?

You can retrieve the shipment item data by shipment item id using Magento 2 by Shipment Item RepositoryInterface.

Used Shipment item repository interface to get shipment data:
Magento\Sales\Api\ShipmentItemRepositoryInterface

An interface contains the get(int $id) method to fetch record by shipment id.

using the above repository, You need to pass shipment item id from the sales_shipment_item table.

Please be careful of shipment_item_id will be used and not the shipment_id from the shipment table.

Pass shipment item id as arguments in the method getShipmentItem() and you can fetch the shipment item as a result.

The output will be from the sales_shipment_item table,

You can get the shipment item record from the item id in Magento 2 with the simple code snippet.

From the above result, you can fetch required data as per your requirement.