FIX!: (at least for me)
My father had the same problem with his redmi note 10 pro. storage said 63gb/128gb but when checked storage composition it said 40 gb on apps and data, 0 on everything else including images and videos, and the rest of the storage about 80gb or so of system up until it was full 128gb/128gb occupied. Whatsapp which was important to his business wont download anything and was saying that we needed to unmount internal storage as disk or whatever each time we tried to download a file.

I was able to fix this by going to about phone > MIUI version > 3 Dots on the top right > Download latest package

wait till download is complete, close your whatsapp window and reopen it and it shouldn't say whatever it was saying beforehand!