Let's get your .IIF file imported to QuickBooks, rmichel.
Before we proceed to any troubleshooting steps, I'd recommend updating the release version of your QuickBooks Desktop.
Then, you can follow the detailed steps in this article on how to get rid of the error in your .IIF file: Improved IIF Import in QuickBooks 2019 and later.
Additional references about the .IIF files are the following:
Feel free to let us know how this goes so we can also review the other options. Additional details about the error would also be appreciated.