@JeZxLee said:
forum is too quiet - great game engine, but not much support?
Well, the forums has been having posts daily, so I'm not sure that counts as quiet. Your post likely has not got any replies because no one really knows what to suggest, or simply they missed the post entirely. A single topic does not reflect the forums nor Godot engine support. Finally, remember that the forums is just one of many Godot communities, and the forums are entirely community run and supported.
To address the OP: I say it depends, but on a whole most games avoid having a exit button because on mobile platforms (iOS and Android), you can just leave the app it and it will be kept in memory. If you want to exit the app, you just leave the app and dismiss it, which kills the app's execution, just like an exit button. For this reason, using an exit button is generally not needed on mobile platforms, as everyone is used to just using the OS to exit and terminate the process.