@OOper thanks for testing. My development environment is: macOS 11.0 Beta Xcode 12.0 Beta iPad Pro (2nd Gen) + iPadOS 14.0 Beta

I tested with my iPhone XS + iOS 13.5.1, which worked fine. Like you said, It's highly likely that it's a bug of iOS 14. Thanks again for your help.

Finally it worked on my iPad too after updating to iPadOS/Xcode beta 2. Actually it didn't work on the first try, then I added one line inside updateUIViewController, and now it works!     func makeUIViewController(context: Context) -> UIDocumentPickerViewController {         let picker = UIDocumentPickerViewController(documentTypes: [kUTTypeImage as String], in: .open)         picker.allowsMultipleSelection = true         return picker     }     func updateUIViewController(_ uiViewController: UIDocumentPickerViewController, context: Context) {         uiViewController.allowsMultipleSelection = true     } The weird thing is it still works correctly even after I remove the line in updateUIViewController... Anyway, thanks for your help @OOPer and @marlonjames.