If your Mac starts up to an Apple logo or progress bar - Apple Support

Your Mac shows an Apple logo when it finds your built-in or external startup disk. As startup continues, you should see a progress bar, with or without the Apple logo. This screen might alternate with a blank screen several times. If you're installing a macOS update or upgrade When you're updating or upgrading macOS, the Apple logo or progress bar might persist for much longer than usual. As installation continues, the progress bar might move slowly and pause for long periods. Apple recommends starting installation in the evening—so that it can complete overnight, if needed. If your Mac is stuck on this screen or keeps restarting If startup never progresses beyond an Apple logo or progress bar: Press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off. (Every Mac has a power button. On laptop computers that have Touch ID, press and hold Touch ID.)Turn your Mac back on. If the issue persists, press and hold the power button until your Mac turns off. Then...