Ways to start up your Mac
Normally you can restart your Mac by choosing Apple menu > Restart. However, in some cases—for example, if the pointer freezes on the screen or your Mac becomes unresponsive—you may have to use a different startup method.
Press and hold the power button on your Mac until it shuts off. After a moment, press the power button again to start your Mac. You may lose unsaved changes in open documents.
Prevent automatic login
When you see the progress indicator, press and hold the left Shift key.
Prevent login items and Finder windows from opening when you log in
After clicking the Log In button in the login window, press and hold the Shift key.
Start up in target disk mode
Use Apple Diagnostics
Select a startup disk
Start up in safe mode
Start up in macOS Recovery
For information about keyboard shortcuts you can use to start up your Mac, see the Apple Support article Mac startup key combinations.