OK, should be fixed in the next release, landing in a couple hours. Godot on Android sends an odd, non-standard scancode for Escape. Its keyboard support is kind of bad in general, actually. I figured out and added that scancode to the action triggered by Escape on other platforms, and in my brief testing (pausing/resuming a game, exiting menus) it did work. Hopefully it does for you too.
I also discovered that, with my PC keyboard connected to my phone, Windows plus Backspace triggered the back button, which does exit the menus. Ugh, pretty bad experience all around, and not sure who is at fault.
Thanks for the reports.