Cannot add new contacts on desktop

Recently I have been unable to add a new contact in "Contacts" on my iMac (BigSur 11.4). I type in a few characters and the app closes. I am forced to go to iCloud, where I can add any contact without issue, after which it appears in my Contacts on my desktop.

I never ever had this issue in the past and I cannot understand why it's happening. Going to iCloud means I have to open it, sign in, get the 6-digit sign-in code, and then I can enter my contact. This is a waste of time.

Does anyone have any idea why this might be happening and how to solve the problem? Thank you in advance.