Hi! I've been using Mi 6 with weekly build for three or four months lately with custom version of GCam. It takes great pictures but since Pie it's not possible to switch to telephoto camera in GCam app. It becomes possible if I turn off SELinux, so I guess you have locked the access to it for other apps. Please, return it! GCam can record video on telephoto camera as well as taking HDR+ and NightSight photos.