Exifs are not saved properly with Image

In my Xamarin iOS App (iOS 15 and later) i tried to save Exifdata in the dictionary with CGImageDestination.Create() and add there the changed Metadata. The data is displayed in the right way in the console, but after saving it with NSData.Save the data is not in the exif anymore, if i write it on the console. I tried changing the CGImageProperties.ExifUserComment and TIFFImageDescription, but both are not saved. Is there any limitation, on which exifdata can be saved or am i doing something wrong? Here is my example code, where i change the existing metadata, set it to the exifdictionary and then save it with NSData.Save().

var img = UIImage.FromFile(file);
NSData ns = img.AsJPEG();

var dicMetadata = ns.ExtractMetaDataFromImageData();
                           
NSMutableDictionary dicDescription = (NSMutableDictionary)dicMetadata.ObjectForKey(ImageIO.CGImageProperties.ExifDictionary);
    if (dicDescription == null)  {
        dicDescription = new NSMutableDictionary();
    }
                            dicDescription.SetValueForKey(FromObject(bf.name.Trim()), ImageIO.CGImageProperties.ExifUserComment);
                            
dicMetadata.SetValueForKey(dicDescription, ImageIO.CGImageProperties.ExifDictionary);
                            
File.Delete(file);
var imgSrc = ImageIO.CGImageSource.FromData(ns);
var outImageData = new NSMutableData();
using (var d = ImageIO.CGImageDestination.Create(outImageData, imgSrc.TypeIdentifier, 1, new ImageIO.CGImageDestinationOptions())) {
        if(d==null)  {
            Console.Write("could not generate dest");
        }
        d.AddImage(imgSrc, 0, dicMetadata);
        d.Close()
}

NSError writeError;
var imageSaved = outImageData.Save(file, NSDataWritingOptions.Atomic, out writeError);