Antinode cannot send data anywhere, because it does not ask Android for the permission to. Everything below follows from that.
The app declares no network permission at all: no
INTERNET, no ACCESS_NETWORK_STATE, in the
app or any library it is built from. A build check fails if either ever
appears in the manifest Google Play receives. There are no accounts, no
analytics, no advertising and no crash reporting.
You can check this yourself. The permission list on the Play Store page, and on the phone under App info, is the manifest, and the manifest is the proof rather than this page.
Audio files and album art on your device, to find and play your music. Nothing is copied off the phone. The library index, play positions and waveform cache stay in the app's own storage and are deleted with it.
Bluetooth, to see which earbuds are connected and what sample rate the link is running at, and to set that rate. On FiiO UTWS5 earbuds it also speaks to the earbuds directly to configure them. The first time you run the app, Android asks you once to allow it to manage the connection to your earbuds.
A notification, so playback has controls on the lock screen and keeps running in the background.
Nothing. No data leaves the device, none is shared with anyone, and there is nothing to delete on request because nothing is held.
If you write to the beta address, the email itself is the only record, and it is used to reply to you and for nothing else.