That sounds like a real challenge. Yep, I'm talking about the app I used to test out MQTT chat. Clone the app from the repository if you're feeling adventurous.
I did put together a tutorial chapter, trying to give at least some information and tips how to get it running on macOS and in the iOS Simulator simultaneously. But here's the kicker—I couldn't crack the Android security issue regarding certificates. Sorry, Android fans, you're on your own with this one.
So, what's the verdict? Well, let's just say this app is tailor-made for the daredevils among us, the ones who thrive on a good challenge. If you've got a knack for troubleshooting and a touch of masochism, then by all means, dive right in. But for the rest of us mere mortals? Maybe stick to apps that don't require a crash course in programming just to send a message.
Now here's a hurdle: I'm not exactly a pro at downloading repositories and making them spring to life with just one magic install command (especially when it comes to this complex amalgamation of Rust, Flutter, Flutter-Rust Bridge, Android, and Xcode). Nope, no hand-holding from me on this one. Proceed at your own risk, folks. You've been warned.
My recommendation: Build the app from scratch as you have learned in the tutorial chapters of IOTA for Flutter. Copy the most important code snippets for Flutter and Rust from the MQTT Chat App repository and paste it into your app.