My nokia 9 recently developed this "pain in the ****" bug. Torch is simply not working, it's grayed out. I cannot turn it on, unless I launch the camera, go to video and turn flash on. If I leave the camera, torch (from drop down menu) works, but only until I lock the phone. On next unlock, torch is again grayed out.
If I install 3rd party flashlight SW it just says "camera not available" until I launch the camera and close it, then it works. But just until I lock the phone, then it's the same again.