Ah, I see what the problem was. Mediafile's page considers the .io file to be a compressed archive. When I saved it with Windows 10/Firefox, the .io file extension was replaced with .zip. All I had to do was change the extension back to .io, and it opened.
I've been waiting for the wing fold to start the Osprey, so hopefully I'll be able to figure out your design. When I was playing with LEGO in my formative years, all they had was bricks, so this Technic stuff baffles me a bit . Do you have a list of the extra parts needed for the wing fold? Or is everything shown in the Studio file needed?
Peter