Transfer QB data files from desktop into Simple Start online version - says "Only open in QB Enterprise Solutions"

Which QB Desktop year version did you have?

You only need to access your data for a single user, correct?

Thank you for visiting the QuickBooks Community, cooperfry. Let me help you find a solution for the migrating issue you encountered. I'll also provide details so you can accurately transfer your data from QuickBooks Desktop to QuickBooks Simple Start.

Beforehand, may I ask as to which QuickBooks Desktop year version you have used? also, where did you access your backup file? Any additional information would be very appreciated so that I can provide accurate information.

Please know that you can only access and restore backup file with the same version. When you back up a file from Enterprise, you can only view it on the same plan that you backed it up on. Furthermore, you also need to access a QBDT when migrating your data to the Online version. If you can't open it, I recommend downloading a trial of QuickBooks Desktop Enterprise. Then, restore your backup file from there. 

Once done, you can open this article to see the step-by-step procedure on how you can import your QuickBooks Desktop company file to QuickBooks Online: Move your QuickBooks Desktop file to QuickBooks Online. 

On the other hand, please know that upgrading to another version of QuickBooks Online isn't needed to be able to see your data. You'll just follow the information stated in the article above to achieve the migration without unexpected errors.

Lastly, I'm also adding this article if you need further guidelines on how to effectively handle your business using QBO: Help guides for QuickBooks Online.

It'll always be my pleasure to help if you have any other concerns besides working with QuickBooks. Please let me know by clicking the Reply button and leaving a comment below. Take care and stay safe, cooperfry.