Apple has two related features, Activation Lock ( Activation Lock for Mac - Apple Support ) and Find My ( iCloud+ - Find My - Apple ), which are designed to prevent anyone else from using a Mac if it's ever lost or stolen. Deactivation of either requires knowing the Apple Account and password that set the feature, or by placing a special request to Apple to reset the device. This Apple Account information essentially defines the current ownership of the device.
If you do not know the required information, are not the signed-in owner, or do not have Apple accepted proof of purchase, get the owner of the account to remove the lock (described in How to remove Activation Lock - Apple Support ), or return the device for a refund, or recycle the Mac. The device is otherwise useless to you. If the owner is unknown and has not provided contact information as a message showing in the login screen, there is no way to contact the owner unless the person who gave you the device knows them.
Here are additional resources if you are the account owner, can find the previous device owner, or have an Apple accepted proof or purchase:
● Read this article to learn how to remove Activation Lock either on the device itself or on the web --> How to remove Activation Lock - Apple Support
or this one for disabling Find My if activation lock has not yet engaged --> Turn off Find My on your devices and items - Apple Support
or if the owner no longer has access to a device it can can be removed from Find My on iCloud.com. as described in this support article Remove a device from Find Devices on iCloud.com - Apple Support --> "You can use Find Devices on iCloud.com to temporarily remove a device from the Devices list or turn off Activation Lock on a device you already gave away or sold."
● Help with a lost Apple ID or password:
• For help with a forgotten Apple ID (this is likely an active email address or one used in the past), click here --> If you forgot your Apple Account primary email address or phone number - Apple Support
• For help with a forgotten Apple ID password, click here --> If you forgot your Apple Account password - Apple Support
● Reset device if you can prove to Apple's satisfaction you are the owner:
Apple can completely reset a device if a person can provide sufficient evidence of valid ownership. This is done online* at: Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not provide many details in the article as to what is acceptable proof. Prior to this official service Apple typically required the original receipt** issued by Apple or an Apple Authorized Reseller and documented provenance (so typically it would be the first owner who does this, or a descendant with legal proof of ownership transfer). Note that while this will let you get use of the device again, it will not help you with lost access to an account.
* There is a special link for this service. To save time you should use it instead of https://getsupport.apple.com/ .
**Apple recommends you keep your receipt after you buy an Apple device. --> Keep your receipt after you buy an Apple device - Apple Support
