Sensible method to edit contacts on a Samsung phone? Currently the Samsung app for Contacts is driving me nuts on my S9+.

I used to have my contacts entered as I wanted them into the Phone address book (only one other phone number on the SIM). But then the Contacts app started to pester me about wanting to merge contacts. Dismissing those notifications by touching that X in the top right of the notification window ended up removing the one contact that was most complete for my significant other (in a sense the master contact which also contained address, birthday, siblings and stuff, aside from the phone numbers). Instead I now have her Telegram and Skype contacts as a single entry in the Contacts app. Alas, that single entry cannot be edited, only deleted. But given the intransparent handling of this stuff, I'm really afraid to delete it, because it warns me that the contacts will disappear from where ever they are defined (so presumably deleting this one entry from Contacts will end up deleting the contacts in Telegram and Skype respectively).

Anyway, so I figured I'd simply start creating a new contact for the Phone app to use, even though the phone number was already mentioned in the combined Telegram and Skype entry.

Guess what, when I create a new entry it cannot be named the same as the existing one, even though the existing one cannot be edited. I'm out of words for how badly this software is designed ...

How can I manage the contacts on my Samsung S9+ in a fashion that makes explicit where a contact is stored (i.e. where the respective data comes from), lets me merge them in either direction and lets me move them between the different address books of connected accounts (SIM, Phone, Google, mail provider)?

NB: I'd like to avoid any method involving syncing to Google or so ...
Try to go into your contacts (in the app you use to phone people), then click a button that says Create Contact and put the number, name, and whatever more info it needs.