I haven't used it for several years and don't remember all the details. But at the very least you need to enter the Game Key and Secret Key in plugin properties. And I think the app id of the project should match Bundle ID in GA.
Perhaps Game Analytics, in addition to not working on PC preview, doesn't even work in the internal test.
No, it should work in internal test. It should even work if you make a debug APK and upload it directly to your phone.
If you are sure that everything is configured properly and GA still doesn't work, you can try getting Logcat logs from your phone. If there is something wrong with GS, there will be an error message in the log.