This will erase your Mac, do you have a good backup?
About Activation Lock on your Mac - Apple Support
If you can't access your Mac and you need to turn off Activation Lock, follow these steps.
- Go to iCloud.com and sign in with your Apple ID.
- Click Find iPhone.
- Select All Devices, then click your Mac.
- Click Erase Mac. Select Next until the device is erased.
- Click
next to your Mac.