Highlight the file and look for the drop down menu , there should be an option that says "rename" and change the file extension that's after the "dot"
(on an iPhone) What I do is select the photo from my photos app, hit “copy”. Then I head over to the files app and hold to paste. Once it posts to the files app, you can hold down the photo and a menu selection will show. Select “Get Info” and it should show that it is a JPEG image. Hope this helps!
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