Rasw photo files imported to iPad Pro Photos are blank

I don't seem to be able to view or edit RAW photo files imported from the SD card into my iPad (Pro M4), they just come up as grey blanks in Apple Photos app!! These photo's are taken on Nikon Z5ii . I am using the SD card reader adapter on the iPad Pro. JPEGs work fine. I was hoping to use the iPad Pro when travelling to import and edit RAW images rather than take my MacBook Pro with me. (they import fine on the MacBook Pro too) Am I doing something wrong??