CIImage generate CGImage is unavailable

Your fontName is incorrect, it's missing an r at the end, it should be @"HoeflerText-Regular".

Adding an r resulted in this image:

Yes, I fix this problem, and UIImage is correct, but actually I still get the nil data to create MTLTexture. But When I load a png file, everything is ok This is my test code:

self.device = MTLCreateSystemDefaultDevice();
   
  // My Text Image
  CIFilter<CITextImageGenerator> * filter = [CIFilter textImageGeneratorFilter];
   filter.text = @"This is a test text";
   filter.fontName = @"HoeflerText-Regular";
   filter.fontSize = 12;
   filter.scaleFactor = 1.0;
   CIImage *image = filter.outputImage;

   CIContext *cicontext = [CIContext contextWithOptions:nil];
   CGImageRef resultRef = [cicontext createCGImage:image fromRect:image.extent];
   UIImage *resultImage = [UIImage imageWithCGImage:resultRef];
  // PNG Image
//  UIImage *resultImage = [UIImage imageNamed:@"nx"];
//  CGImageRef resultRef = resultImage.CGImage;
    
   CFDataRef data = CGDataProviderCopyData(CGImageGetDataProvider(resultRef));
   const unsigned char * buffer = CFDataGetBytePtr(data);
   
  CGFloat width = CGImageGetWidth(resultRef), height = CGImageGetHeight(resultRef);
  NSInteger bytesPerPixel = 4, bytesPerRow = bytesPerPixel * width, bitsPerComponent = 8;
  CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
  void *rawData = calloc(height * width * bytesPerPixel, sizeof(uint8_t));
  if (rawData == nil) {
    CGColorSpaceRelease(colorSpace);
    colorSpace = NULL;
  }
  CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast|kCGImageByteOrder32Big);
  CGColorSpaceRelease(colorSpace);
  colorSpace = NULL;
  if (context == nil) {
    free(rawData);
  }
  CGContextTranslateCTM(context, 0, height);
  CGContextScaleCTM(context, 1, -1);
  CGContextDrawImage(context, CGRectMake(0, 0, width, height), resultRef);
   
  MTLTextureDescriptor *textureDescriptor = [MTLTextureDescriptor texture2DDescriptorWithPixelFormat:MTLPixelFormatRGBA8Unorm width:width height:height mipmapped:NO];
  id<MTLTexture> texture = [self.device newTextureWithDescriptor:textureDescriptor];
  if (!texture) {
    free(rawData);
    CGContextRelease(context);
  }
  MTLRegion region = MTLRegionMake3D(0, 0, 0, width, height, 1);
  [texture replaceRegion:region mipmapLevel:0 withBytes:rawData bytesPerRow:bytesPerRow];
  free(rawData);
  CGContextRelease(context);
  _fontTexture = texture;

Thank you very much!

This is my test image named nx

It renders as expected. However your texture background's is black just like your text colour. Because CGContext is premultiplying alpha.

If you change the context's background to red for example, you will see it.

CGContextRef context = CGBitmapContextCreate(rawData, width, height, bitsPerComponent, bytesPerRow, colorSpace, kCGImageAlphaPremultipliedLast|kCGImageByteOrder32Big);
CGContextSetFillColorWithColor(context, [[UIColor redColor] CGColor]);
CGContextFillRect(context,  CGRectMake(0, 0, width, height));

To bypass CGContext all together, try rendering directly to an MTLTexture using CIContext's render(_: to: commandBuffer: bounds: colorSpace:), you can find more info here: Apple Developer Doc