https://www.dekut.com/Questions/how-to-fix-a-macbook-flashing-file-folder-with-a-question-mark-at-start-up/ A folder with a flashing question mark means that your startup disk is no longer available or doesn't contain a working Mac operating system. If the question mark appears only momentarily before your Mac starts up normally: Reset NVRAM. Make sure that your preferred startup disk is selected in Startup Disk preferences... Wed, 30 Dec 2020 05:00:43 UTC en