According to the Xbox Insiders page on reddit ( windowsgaming - xboxinsiders (reddit.com)):
If you want to roll back to the stable version of the Xbox App then you will need to leave the preview.
- Ensure that you signing in to the Xbox App, the Windows Store and the Xbox Insider Hub with the same account.
- Load the Xbox Insider Hub, find the Windows Gaming preview in your 'Joined' list. Click Manage. Scroll down and click Leave Preview
- Ensure that you are properly removed from the preview. Windows Gaming should now be listed in the available list
- Remove the Xbox App using Windows Settings > Apps (find Xbox App and uninstall)
- Remove Gaming Services. In Windows PowerShell, type the following command and press Enter: get-appxpackage Microsoft.GamingServices | remove-AppxPackage -allusers
- Reboot PC
- Load the Windows Store, find the Xbox App and install.
When you are not part of the Windows Gaming preview, the Windows Store will deliver the stable public build of the Xbox App. It will only deliver the preview version if your account is part of the preview group.
It's a bit of a process to do so, it won't automatically revert. Hope that helps :)
-Hayabusa