I'd like to set my macOS app written in Swift as default app when opening .mp4 file. I think I can do it with setDefaultApplication(at:toOpen:completion:). https://developer.apple.com/documentation/appkit/nsworkspace/3753002-setdefaultapplication However, permission error occurs when I use it. The error is: Error Domain=NSCocoaErrorDomain Code=256 "The file couldn’t be opened." UserInfo={NSUnderlyingError=0x6000031d0150 {Error Domain=NSOSStatusErrorDomain Code=-54 "permErr: permissions error (on file open)"}} I tried to give my app full-disk access, but it didn't work. I also tried to use setDefaultApplication(at:toOpenFileAt:completion:), then it works with no error, but it effects on only one file. What I want to do is to set my app as default app of all .mp4 files. How do I achieve this? My code is like below: let bundleUrl = Bundle.main.bundleURL NSWorkspace.shared.setDefaultApplication(at: bundleUrl, toOpen: .mpeg4Movie) { error in print(error) } Thank you.