Transferring RAW DNG photos shot on iPhone is taking very long as it takes a long time for MacBook to read

Hello, I have a rather confusing problem that seems to be impossible to resolve. For a while now, at least since March, I think, of this year, I've been having problems transferring RAW images from my iPhone to my MacBook Pro. It does not seem to be a size issue as video files of large sizes can be immediately read by Image Capture and Photos but RAW DNG from the iPhone takes a long time to be read. For example, in the past, if I had shot, say, 1000 RAW images in a day on the iPhone, I will plug it in and the MacBook immediately reads it. But now, when I plug it in, it takes a very long time for the MacBook to read the entire set of images even though they are there on the iPhone. Basically, plugged in continuously, it will take a large number of hours for the MacBook to read all the images that are on the phone, specifically the RAW DNG images. The ones in HEIC and JPEG do not suffer this issue as are the large video files in the highest resolution which makes me think this is an issue with RAW DNG.

Another thing about this problem is that the phone needs to be plugged in for the images to be read and makes me wonder what the underlying issue might be that is crippling the time needed for it to be read. I tested it on both the iPhone XS Max and iPhone X and also tested it with another MacBook as well, both on Catalina. I wonder if anyone suffers from this problem or could test it out on their own and see, even with 100 images, you would be able to see the lengthy time it will take for all images to appear. I would appreciate if anyone can help regarding this. I have also reformatted fully the iPhone and MacBook Pro to see if there is something in the software that is causing this but nothing doing, the same problem persists even after the reformat.