Ways to start up your Mac
Normally you can restart your Mac by choosing Apple menu > Restart. However, in some cases—for example, if your Mac becomes unresponsive—you may need 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 the progress indicator appears, 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
See Transfer files between two Mac computers using target disk mode.
Use Apple Diagnostics
Select a startup disk
Start up in safe mode
Start up in macOS Recovery
See Use macOS Recovery on an Intel-based Mac or Use macOS Recovery on a Mac with Apple silicon.
For information about keyboard shortcuts you can use to start up an Intel-based Mac, see the Apple Support article Mac startup key combinations.