I also tried to pair my DS4 to my A70, and I observed the same problems. Both devices seem to be connected (the DS4's light bar stays lit and One UI displays "Wireless Controller - Connected"), but none of the apps I tried reacted to my controller's input. And trying to disconnect the devices causes the bluetooth to be unusable until I restart my phone. I think that, according to this XDA article, a missing key layout configuration shouldn't be the cause of this problem in Android 9. Yet, this is my first device where I'm unable to use any of my DS4 controllers.
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