Since plugin version 3.9 (min UE4.27) the plugin also works on mobile platforms (only Android tested).
Android uses the NDK API. IOS uses the Unreal functions. There are some limitations. Especially under IOS. I can't 100% confirm that IOS works at all. See IOS as "better than nothing" and no more.

The following work on Android.
Buttons
Axes
Connected and disconnected detection
Device Name
Battery
Rumble. Android has only supported rumble via Bluetooth since version 12. With older Android versions, the controller must be connected via a cable. I tested it with Android 14 and an Xbox gamepad.

IOS

If you use IOS you have to start the plugin.
Important! One playercontroller per gamepad is required. However, one playercontroller always exists anyway.
But if a second gamepad is connected, the plugin automatically creates another playercontroller.
I recommend doing this in Gamemode blueprint.

Unreal only fires the events if the input mode is set to Game or Game and UI. Screenshot from Levelblueprint of the demo project.