Hello! I am attempting to do an Inventory Adjustment CSV import. I have got everything mapped; however I keep getting an error that tells me the internal ID (or external if I switch it) for that record cannot be found. Should I be using the internal ID of the inventory items I am trying to adjust? I know they are right I have verified them multiple times

Apologies if this seems like a redundant answer but I've seen people do this before. The internal id you map for the items is not the internal id field listed in the import manager fields (right-hand pane). You don't map that as that is the internal id for the transaction. Instead map the item internal id field in your file to item, click the pencil icon next to the field mapping, and then select internal id in the additional drop-down.

It does not recognize the item if I use the internal ID. If I click the pencil and then drop down for the Item mapping, it brings me to a search of inventory items.

First you have to map the fields internal item id -> item. Then, under the additional options, switch the reference type from Names to internal id