You need to grant access to all files and not just media files for the camera app. It will not ask it so you need to long press the app, choose i or whatever your launcher suggests to see application information and there you should be able to modify rights.hi , i get this problem when double-click to add xml. ( Device out of storage )
On my oneplus7pro, Andoid 11
Also you need to have GCam\Configs8 or similar path already on the phone where camera app can select config file.