Possibly it's not been released yet, although android still shows as coming soon too.
The TalkTalk Mail app is available in the Google Play Store and, like you, I'm running it on an Android 9 mobile and also here on Android 7. My understanding is that the app is not available for every device. The compatibility note does not indicate which versions are being supported in this 'early access' Version 1.
The vendor's own branded software, now on Version 2.24, works with Android 5 and up but is not usable with TalkTalk Mail.
Hi all, when I last checked development was temporarily on hold due to Covid19. I've not been able to get more specific information.