Thanks for the response. I only used a comment because the forum displayed an error when I tried to reply. But writing a comment worked. Probably just bad timing. Anyway: I tried com.apple.security.temporary-exception.files.absolute-path.read-write with / and it worked. Nice. A few days ago I saw this older post: https://developer.apple.com/forums/thread/779672 which has a similar question. My issues might even be better solved with FSActivateOptionSyntax, but I don't know where to find the docs for it. Or how to propably use it. I was also able to use logs again. Don't know what was wrong. The only question remaining is: The test question. I started to write basic test, but it is really hard. I even had to use an ugly hack https://github.com/TheNoim/fskit-unionfs/blob/e8beb6598dec62365d096f834e6eec425386edef/FSKit-UnionfsTests/TestHelper.swift#L31 because sometimes after rebuilding the extension the fskitd daemon failed to start the extension for some unknown reason.