macOS Contacts hasn't changed significantly in years. The way you show where you contacts are is to, in the Contacts app, make sure that the "Lists" are shown (menu item View>Show Lists).
Sounds like you have 441 contacts in iCloud, 363 in some other list (probably under "On My Mac") on the Mini and 399 in some other list on your MBA.
I don't know of a magic way to fix duplicates. Perhaps someone else does. I haven't dealt with that issue in many, many years.
Set your default account, in Contacts preferences, to iCloud on your Mini and your MBA to prevent newly created contacts from going to some other list.
Thanks, I should have mentioned that I did check out Lists before posting, which only resulted in more uncertainty.
First, the Lists appear differently on my Mac mini vs. MBA. Both are updated to Ventura 13.2. 2ndly, only the MBA shows the "On My Mac" option. 3rd, when selecting On My Mac on the MBA, only my contact shows up.
Mac mini shows:
iCloud > All Contacts --> 820 contacts*
Smart Lists > Last Import --> empty
*I believe this was 804 just 1 hour ago, so yet another mystery here. I have been monkeying around with contacts for a day or two and not sure why it would suddenly change. But my iPhone/iPad still shows only 441)
MBA shows:
iCloud > All iCloud --> 840 contacts
On My Mac > All On My Mac --> this shows only my contact card info, and with a different icon than when looking at the same contact under "All iCloud"
Smart Lists > Last Import --> empty
But as far as selecting the account(s) on my Mac mini & MBA, I have "Enable this account" selected only for iCloud CardDAV. None of my other email accounts have that selected. However I'm not sure what you mean by selecting a "default account" in the Contacts Preferences.
Thanks for the (ongoing) help !