After switching your controller into Bluetooth mode, press and hold the “Y + Stadia” buttons for 2 seconds to enter pairing mode. The status light will flash orange. Then, go to the device you want to play on and pair your controller in the settings.

begin Bluetooth pairing by pressing and holding both the 'Y + Stadia' buttons for two seconds (the status light will flash orange) then go to the device you want to play on to pair it with your controller in the settings (once paired/connected, the status light will turn solid white)

You may also try to reboot your devices and try to re-pair it. If the issue persists and this is only happening when using the Google Stadia controller, please perform a factory reset on your Stadia controller. You can also visit the Google Stadia Help Center for additional help.

Stadia is discontinued and by extension, so is the controller. At this point, if you want the best compatibility with almost every device and future updates and support, your best bet would be to get an Xbox controller.