QB Issue Resolution:

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 exported back. Round tripping is not a good idea, data lossed in both directions

Resolution for Issue 'QBXML Conversion' available: Yes (Solved).
Source: Intuit Community forum.

QBXML Conversion: this 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 issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

Support for conversion file
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Error Recovery for conversion file [Canada]
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