Q: Every time I use MC, the permission to paste between iPhone and MacBook will pop up, how to cancel?

A: This is because that the ID of your mobile phone and the ID of your Apple computer are the same, and then they are synchronized, you can turn off the "Handoff" function in the phone settings. 

On iPhone/iPad/iPod touch: Go to Settings → Tap General→ AirPlay & Handoff → Turn off "Handoff"

On Mac: Go to Apple Menu → Click System Preferences→ General, then turn off  “Allow Handoff between this Mac and iCloud devices”