When you install macOS or turn on a new Mac, your Mac automatically starts up to a setup assistant, which asks for details such as your country, language, Wi-Fi network, and more. The final stage of the setup assistant is Setting Up Your Mac:
This stage should take no more than 10 minutes to complete. If it never completes, your Mac might be unable to quit the setup assistant, even though setup is complete.
To resolve, press and hold the power button on your Mac for up to 10 seconds, until your Mac turns off. Then turn your Mac back on. Your Mac should now start up normally.