iReal Pro is not specifically a cast-enabled app, but some Android (only) devices (for example, some models of Nexus, Galaxy, LG and Sony) can cast (mirror) the screen or audio so it should be possible. We have not tested this extensively on these or any other devices.
For more information check out Google’s Chromecast site for the Android devices that can mirror screen and audio.https://support.google.com/chromecast/?hl=en#topic=6314574
Here you find the basic steps - we tested it and it worked fine:
In case you don't hear the audio, connect and disconnect the Cast Screen/Audio within the Google Home App, then start iReal Pro and in the Google Home app, select Cast Screen/Audio.