How do I import a contacts list from one iMac to a new iMac?
How do I transfer a contacts list from an iMac desktop to a new iMac desktop?
iMac (24-inch, M1, 2021, 2 ports)
One option is to turn on iCloud Contacts on you old iMac and your new one and they will automatically sync. Set up iCloud for Contacts on all your devices - Apple Support
Another would be to open the Contacts app on the old Mac, use File menu > Export > Contacts Archive and then transfer that archive file to the new Mac and use File menu > Import