Check if you can change button layout in the game options/settings.
If not you should be able to do this via the Controller Configuration tab, from the In game steam overlay.
From their you can swap and change all sort of stuff for your controller and save different layouts for different games.

However, that function seams to have broke completely with the latest update for some ppl. (Me included XP ) So if you can't get the controller configurations to work. You probably have to wait for steam to sort out the bug.

If your desperate you can try a program called JoyToKey. (Google it) It can be a bit wonky to set up though. So no promises their.

Hope that helped :)

After launching the game in your client, click the menu on the right side across from the Play/Stop button and look for something like Manage > Controller Layout. The option will not be there if the game hasn't been launched but should appear as soon as it starts running.

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Did you manage to resolve this? If yes, how?

I was able to manually assign R1 to R2 and visa versa, but now the buttons are a double input. Pressing R1 reads R1+R2. It's as if Arc Raiders is reading my raw PS4 input and also my reconfigured steam input.