My contacts in Messages are not syncing on my new Mac I just got a new Mac and my contacts are not syncing in messages. I have turned off/on contacts sync on both the new Mac and my iPhone multiple times, but the issue persists.
Please note, not all my contacts are missing on my Mac, but most of them are. Certain contacts like my immediate family members are shown in Messages....not sure why. When I search in the Contacts app in my Mac, I do not seeing the missing ones. I can add them one-by-one, but obviously this is not a good solution.
How can I fix this?
EDIT: I'm on macOS Mojave and cannot upgrade yet because I must have some legacy 32-bit apps. However, iTunes has the sync functionality that was moved into Finder in Mojave (iTunes has been EOL'd, thankfully).
You can try following method

Connect your iphone or iPad to your mac using a usb cable.
Wait a few minutes and then open a new Finder window.
Your device should appear in the Sidebar of your Finder window.
Select your device and you should get a panel like the one below.



Click on info on the top line of your panel.

This should give you options on which things to sync. This method is described in more detail at this location