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.

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?