I found that some apps I installed from AppStore can import multiple files by Share extension or Action extension. But since I need to access CoreData database, I think it will be better to just open my main app to handle file importing.

Conditional views in columns of NavigationSplitView fail to update on some state changes. (91311311) Workaround: Wrap the contents of the column in a ZStack. See iOS & iPadOS 16 Beta 3 Release Notes