Thanks for bringing this idea to our attention, @jcd4. Let me help you convert your files in QuickBooks Desktop (QBDT). 

We're unable to directly convert the QuickBooks Online (QBO) file to an IIF file format in QBDT. However, we can convert QBO files to IIF by using a third-party app. This will allow you to convert the file type. That way, you'll be able to import into IIF files in QuickBooks Desktop (QBDT).

Once done, ensure to back up your QuickBooks data file before any IIF import and choose a bank from the Chart of accounts where you can import the IIF file format.

Here are the following steps:

1. Go to the File menu, then select Utilities.
2. Click Import, then select Import IIF file.
3. Choose the IIF file you want to import, then select Open.
4. Select OK to confirm.

You can refer to this link for more information about the maximum number of lists you can make and different types of files to store different types of data and also how to import and export IIF files:

• Export, import, and edit IIF files.
• Maximum number of list entries (list limits and custom fields.
• File types and extensions used by QuickBooks Desktop.

Also, you can check this article to learn how to create rules to help QuickBooks match your Bank Feeds transactions in QBDT: Create rules to categorize transactions in QuickBooks Desktop.

If you have other questions about importing files in QBDT, please leave a reply in the comment section. Keep safe.