Any luck? I have a machine that I just updated to 10.13.4 and clicking "Allow" still does nothing for enabling the smart sync extension.
EDIT: I was trying to do this via VNC to a mac that did not have a display, keyboard, or mouse attached. Once I attached those items, I was able to click the "Allow" button. Apparently you cannot click that button from a VNC session. Lesson learned.
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