Back up your data if possible
Shut down the MacBook
Press and hold the Power button for 10 seconds
Release the Power button
Wait a few seconds
Press the Power button again to turn it on
If needed, reset NVRAM by turning it on and immediately holding Option + Command + P + R for about 20 seconds
If needed, reset the SMC on Intel MacBook models using the correct key combination for your model
If needed, enter macOS Recovery by turning it on and holding Command + R
In Recovery, choose Disk Utility if you want to erase the MacBook
In Recovery, choose Reinstall macOS if you want to reinstall the system