PHImageResultIsDegradedKey/PHImageFileURLKey is not found

You have to use this function from PHAsset object:

- (PHContentEditingInputRequestID)requestContentEditingInputWithOptions:(nullable PHContentEditingInputRequestOptions *)options completionHandler:(void (^)(PHContentEditingInput *__nullable contentEditingInput, NSDictionary *info))completionHandler;

Then you can retrieve URL this way:

NSURL *url = contentEditingInput.fullSizeImageURL;

Some example Objective-C code for anyone else looking for it:

PHContentEditingInputRequestOptions *editOptions = [[PHContentEditingInputRequestOptions alloc] init];

[myPHAsset requestContentEditingInputWithOptions:editOptions completionHandler:^(PHContentEditingInput *contentEditingInput, NSDictionary *info) {

    if (contentEditingInput.fullSizeImageURL) {
        //do something with contentEditingInput.fullSizeImageURL
    }

}];