Unable to switch off Prime 4 Controller after firmware upgrade

[JustMe]

Try doing what this guy posted if you are able to?

Prime GO bricked after 2.1.1 Update

To re-do the firmware upgrade by cable: Download the PC or Mac version of the firmware upgrade and connect the Blue USB cable. Connect the power adapter and press the ON button while holding LOAD > and LOAD < buttons to enter firmware update mode on the Prime Go. Now run the firmware upgrade program on your PC/Mac.