Transfer files between two Mac computers using target disk mode
If you have two Mac computers with USB, USB-C, or Thunderbolt ports, you can connect them so that one of them appears as an external hard disk on the other. This is called target disk mode.
Note: If either of the computers has macOS 11 or later installed, you must connect the two computers using a Thunderbolt cable.
Connect the two computers with a USB, USB-C, or Thunderbolt cable.
On the Mac you want to use as the external disk in target disk mode, do one of the following:
If the computer is off, start it up while pressing and holding the T key.
If the computer is on, choose Apple menu
> System Preferences, click Startup Disk 
, then click Target Disk Mode.When the computer has started up, a disk icon appears on the desktop of the other computer.
Transfer files by dragging them to and from the disk.
Eject the disk by dragging its icon to the Trash.
While you drag, the Trash icon changes to an Eject icon.
On the Mac you used as a disk, push the power button to shut it down, then disconnect the cable.
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