There are more types of files than Jpegs for photography.
People who process photographic files not only want to download Jpegs, but also RAW fies (for processing), files created by processing software such as Lightroom, Photoshop, Affinity Photo,Dxo.
NONE OF THESE CAN BE DOWNLOADED TO A MOBILE DEVICE.
OS5 is a car crash and now I’m stuck with it.
I suggest that you WD get rud of OS5 and replace it with something that allows the transfer/copying of more than Jpegs to a mobile device.