I too struggled with this very same issue, for a long time, for both Android and iOS apps. App Store Connect and Google Play really need to add support to webhooks!! 😡

The solution was to use the Publishing API aforementioned by @Tom Benyon, alongside fastlane, fastlane_core and supply, to determine the current app's publishing status (my exp as a core contributor at fastlane definitely helped), and keep polling their API.

The problem is that Google's API isn't precise enough: sometimes it will say the app status is "completed" (aka app has been "approved"), even though it's still under review, actually. Which sucks. This is a known limitation and is being tracked in Google Issue Tracker, but Google hasn't promised when they'd fix this.

I was able to work around this limitation though, and get precise status updates throughout time 🎉

If you don't want to build all of this logic yourself and skip the hosting infra shenanigans, I've wrapped this as a service at Statused - feel free to check it out

If you don't want all this precision though, and a ~24-hour delay in the status is acceptable, you'll do fine by using fastlane to get the app status, let me know if you need help with that! For Statused the delay is about 2 minutes, so you get nearly instant updates about when your app status change and can receive those notifications via Slack or custom webhooks to trigger your system's automations as you wish