How do I unlink a MacBook from my iCloud and iPhone?

1. Open the Settings app in your iPhone.
2. Tap on your name.
3. Scroll down and you'll be able to see all the devices that are linked to iCloud.
4. Tap the one you want to delete unlink your iCloud from.
5. Scroll down and tap the red button that says somethink like "Delete from account" or "Remove from account" or something of that sort.

Important note: iCloud is directly tied to your Apple Account, so by doing the previosly mentioned steps you will also sign off from your Apple Account, which means you will not be able to use any services or apps that require an Apple Account, like the App Store, iMessages and FaceTime, the 'Find My' app which allows you to track your Apple Devices if lost/stolen, or any other connection-based Apple Service.