Issues with the Keyboard overlay

Ok, so after a lot more digging, the keyboard close button bug is an issue with Unity's TouchScreenKeyboard implementation. 

The status property of this doesn't change when pressing the keyboard close button. You'd expect this to change to Canceled or LostFocus or even Done, but it just doesn't change from Visible.

Both the Unity UI & TMP Input field code rely on this property and so explains why they both fail / do nothing in the same way.

The Java code for Unity's TouchScreenKeyboard native implementation for Android isn't easily available / readable / replaceable but luckily I had already developed our own replacement for this in our standard Android app. For some reason I thought this wouldn't work on Quest, but the Quest keyboard is actually a standard Input Method Editor so works with my implementation too 🙂

To be fair to Unity, detecting the Android keyboard closing is not as simple as it sounds, but after lots of failed attempts, I've got a working solution by polling InputMethodManager.isActive passing in the EditText field as the view.