Why are files in the Shared folder automatically copied to other Macs? I have an iMac and I'm trying to use the folder /Users/Shared to share files between different users of that iMac. When I copy something large to that folder two things happen


The iMac slows down a lot
On a macbook that I also own (same network, logged into same iCloud account, ...) there is a popup "pasting X items from iMac" and it seems to initiate a copy over the network


What is this?  Why is copying to the /Users/Shared folder initiating a network copy, and to where?

File Sharing (and all other sharing options) are disabled on both the iMac and the Macbook.
This isn't anything specific to the Shared folder, but rather because you're using the clipboard to copy files there.

When you copy something such that it is placed on the clipboard, Universal Clipboard allows those files to be pasted anywhere across any of your devices logged into the same iCloud account, including iOS devices and Macs.

To disable this functionality, disable Handoff in System Preferences → General → Allow Handoff between this Mac and your iCloud devices.

macOS Sierra: Copy and paste across devices