Just tested, had to sync it to my phone by holding the PS button and the share button down for five seconds to put it in sync mode, then opening Bluetooth on phone and adding it. It showed up as just "wireless controller" in the list of devices. Once I did that I was able to fire up the PS Remote Play App, it turned my PS5 on and connected to it, and the controller worked like a charm. Maybe check the device in your Bluetooth settings and make sure it's enabled as an input device?