I also have a controller with an unresponsive ZR button. I read on another post that taking it apart and cleaning the electronic contact under the button can sometimes solve the issue.. I haven’t tried it yet, but will update this thread when I do.

If you can’t get your Power A Enhanced Wireless Controller to pair with your Nintendo Switch, try restarting your Nintendo Switch. As soon as I restarted my Switch, the controller pair instantly when following the pairing instructions provided with the controller. Hope this helps.