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.
Do u know how to rest my ps4 button when I connect it to my Samsung galaxy s9+ back to normal like my buttons are mess up its square to click on something instead of x