Tap the pen in the small toolbox, it should turn orange [on] and display the larger box. Or are you saying the pen box just doesn't come on when the pen icon is tapped.
Dell Latitude 13.5" 2-in-1 Ubuntu/Win 11
Samsung Note Pro SM-P900 12.2 Android 5.0.2
Samsung S7+, Android 12
Samsung Note Pro SM-P900 12.2 Android 5.0.2
Samsung S7+, Android 12