The import instructions (below) include a link to the current QBDT.  You can install it (don’t try to register it) and try to restore your backup file.  If the 2 versions are not too different in age it should work.  You can then import into QBO.

https://community.intuit.com/articles/1350481-import-data-into-quickbooks-online-from-quickbooks-des…

Resolution for '2 versions issue: 'import data to online QB from old desk top version with back up from a thumb drive only' available: Yes.

The 2 versions 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 2 versions issue yourself by looking for a resolution described in the article. If it is a complex 2 versions issue or you are unable to solve the issue, you may contact us by clicking here or by using other 2 versions support options.

For more information about resolving issues related to 2 versions in Quickbooks/QBO or to get support for the issue 'import data to online QB from old desk top version with back up from a thumb drive only', click the link below: