It’s certainly possible. You would need to periodically poll the Get Streams endpoint (for example, once a minute) and request that specific streamer. When they’re offline you’ll get no data, or when they’re online you’ll get the data about their stream.
Alternatively, a more responsive approach would be to use EventSub and subscribe to the stream.online and stream.offline types, which would mean Twitch will send you notifications when the stream goes online. EventSub does require hosting a HTTPS server though, that’s accessible to the internet, so this solution may or may not be an option depending on your circumstances.
As to how your app would alert you once it got the information that the stream is online would be entirely up to you to devise.