Hi there, David.

Let me clarify things about importing IIF from QuickBooks Desktop Enterprise 2023 to QuickBooks Desktop Premier 2021. 

Different editions of the application are designed to cater to different business needs and requirements, aligning with your company's size, industry, and accounting demands.

Each edition obtains features that one another might not have or the other way around. Therefore, importing your QBDT Enterprise 2023 file to an older version and different edition is inapplicable.

In this, you'll want to manually re-enter the transactions you entered from the later version into the old one. As an alternative solution, you can also use a different application.

Furthermore, I suggest scanning this article to learn about QuickBooks Desktop company file compatibility. This will help you avoid issues and errors when upgrading: Company file compatibility with QuickBooks Desktop when upgrading.

Let me know if you have further concerns with your QBDT company files by leaving a comment below, David. I’ll be here to assist you anytime.