You are looking at the wrong file type. That is not a QBO to Desktop conversion file. Therer is no QBO backup. Proper andn only procedure to get Online to Desktop is here.

https://community.intuit.com/articles/1145829-exporting-your-data-from-online-to-desktop

 

What you get is not a backup of Online, although it can be […]

Resolution for 'conversion file issue: 'QBXML Conversion' available: Yes.

The conversion file issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the conversion file issue yourself by looking for a resolution described in the article. If it is a complex conversion file issue or you are unable to solve the issue, you may contact us by clicking here or by using other conversion file support options.

For more information about resolving issues related to conversion file in Quickbooks/QBO or to get support for the issue 'QBXML Conversion', click the link below: