Hi @Shawn Kesinger,
Thank you for posting in this community.
You can upload your master inventory list and the scanned CSV file into SharePoint as two lists. All we have to do is determine which ones have not been scanned by comparing the items' serial numbers in the two lists.
1.You can choose to create the list via excel sheet or CSV files. In this test I am creating two list tables Master Inventory List and Scan List for example.
2.You can refer to this article to use Power Automate flow to compare the differences between the two lists: Compare two SharePoint Lists.
If the answer is helpful, please click "Accept Answer" and kindly upvote it. If you have extra questions about this answer, please click "Comment".
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.