Hello,
Since this is posted in the Ribbon forum, I assume you're using the legacy Ribbon product and not the newer Ribbon in our Bars product that is replacing it?
I pulled up our legacy Ribbon and showed the main demo's Backstage. Using the Accessibility Insights for Windows app, I was able to see the Backstage close button show up properly in the UIA tree, from where it can be invoked. We do not use Test Complete though, so I'm not sure what logic that application uses to locate elements.
To be thorough, I also checked the same thing in the newer Bars Ribbon demo and saw the close button in the UIA tree too.
Both of these tests were in the latest 23.1.3 version. If you are on an older version, you may want to try upgrading since we have made UIA improvements over time to our products.