Hey, thanks for your answer! I researched about the topic using the docs, and have attempted to implement it. I am now accessing the URLs using FIFinderSyncController.default().selectedItemURLs() and then create a bookmark for every url using the bookmarkData function. Unfortunately with the error "Could not open() the item" (code 256), do you have any idea how I could fix this?

Hey, thanks for your answer. Yes, selectedItemURLs() is returning a value. The whole startAccessingSecurityScopedResource() workflow does not work, because the operating system thinks that the provided urls are not selected by the user selected (and therefore not available to the sandbox). I am pretty sure that this is an issue of the operating system not recognising that these files are indeed user selected and should therefore be accessible to the extension.