Old MAC

  With the release if the M1 Apple chip MACs you may have or plan to upgrade your MAC hardware. You have value in your old ro replaced hardware. 

 Before you do gift, recycle, or abandon your older hardware be aware the security of MacOS from Mojave on may prevent use by anyone else. This is the helpful <-> harmful aspect of most cyber security. If your MAC is stolen or misplaced you do NOT want others to access the data stored on that MAC. But you do want to put the hardware to use in an environmental responsible way.

 Step one. Sign out on the old hardware. Sign out of iMessage, iTunes, iCloud, and amy applications where you authenticate with your Apple ID.

BE SURE you are ready, really ready to proceed. After these next steps you will be able to recover. After these next steps others will not.

 Consider unpairing any Bluetooth devices.

To erase and re-install MacOS:

Shutdown and boot the MAC while holding down the Command + R keys                            Select the Disk Utility 

Select the system disk 

Click Erase 

Provide a name for the disk    consider APFS for the format

Erase any other internal disks and any Volume Groups 

Disable Find My if that ability was enabled 

After the format is complete quit the Disk Utility and select Reinstall MacOS from the utilities window.

After the re-install completes:

Next clear parameters you have set that are stored in the MAC hardware. These settings can be used to recover MACs for forensics. 

 Shutdown the MAC   Power on with the Option + Command + P + R                                      Not easily done  On purpose I would imagine                                                                            You will know if this step erased the settings in NVRAM and parameter RAM if your parameters are no longer available.

 Your MAC should boot into a fresh install of MacOS