NVRAM is memory to which your Mac saves settings that it needs before loading MacOS: things like screen resolution, time zone, volume level and startup-disk selection. Go to System Preferences > Bluetooth, mouse over the device you want to unpair, click the X button to the right of its name, then click Remove. If you're handing down your old Mac to your kid or someone else in your house, then it's a good idea to unpair any Bluetooth devices from it so your mouse or keyboard controls the new Mac and doesn't interfere with the old one. Open the Messages app, go to Messages > Preferences, click the iMessage tab and then click Sign Out. Lastly, you'll need to sign out of Messages. Next, click Overview from the left panel and then click the Sign Out button. Go to System Preferences > Apple ID, click iCloud in the left panel and then uncheck Find My Mac. Next, you'll need to turn off Find My Mac and sign out of iCloud. You'll need to enter your Apple ID and password and then hit the Deauthorize button. Open up any of those apps and go to Account > Authorizations > Deauthorize This Computer. Years ago, this was done using iTunes, but you now must individually sign out of three apps - Music, TV and Books. First, you'll need to sign out of all of your accounts. After migrating your data to your new Mac or making one last backup to preserve your data, it's time to remove all traces of yourself from the machine.
