Problems with the 'Contacts' app on the Mac
Adding a new card or a new contact has been problematic. As soon as I enter a name or phone number, the app jumps back to my first contact without saving the one I was entering.
I think i have resolved the issue - it's a little strange but it seems to work.
1) click on create a new contact / new card
2) enter the first name, and immediately
3) go to 'SAVE'
It will save that contact. All you have to do then is edit it, and re-save.
Hope that works for you to.
Cheers, Alain.
iMac 24″, macOS 14.2