I’ve noticed that whenever someone posts a Show HN and the only way to try it is by downloading a native mobile app (especially from the Apple App Store) it tends to get significantly less feedback. The friction of having to install an app, plus the fact that it’s limited to iPhone users just slashes engagement.
If at all possible, consider building a PWA for the beta. You’ll get a lot more eyeballs by making it accessible as a simple website. Then once things are more polished, you could migrate over to a dedicated app.