I got your back, @capplum260.
For the time being, the types of files that are available to import into QuickBooks Online (QBO) are CSV, Google Sheets, and XLS/XLSX.
Nonetheless, the option I can provide is to search for a third-party application. This way, you’ll be able to find the perfect software to utilize and convert IIF to any of the above-mentioned approved file types. You can also look for a third-party tool that can import the IIF file directly into your QBO account.
You can go ahead and browse this website for a complete list of third-party apps that you can sync with QBO: QuickBooks Apps Store
Keep this article for reference: Common questions about importing data to QuickBooks Online.
If you need further assistance to import your files, you can always ask me here in the Community. I’ll be around the corner to help you. Stay safe!