How to remove phone numbers from a contact when they are not visible in edit mode?
Short on ideas I decided to delete this contact.
Right after it was deleted, ANOTHER contact with the same name appeared out of nowhere, holding the two Japanese numbers (and only this, plus the first name, plus the family name).
I then deleted that second (invisible so far) contact and recreated one for my friend (with only the French number).
It worked and I have one single contact.
This is really a mystery to me: I had one contact for that user previously, and the other one only appeared when I erased the first one.
I exclusively store contacts in google (not in the SIM or anywhere else) so this is not a traditional &quot;merged contact&quot; view. My wild guess is that Signal must have kept is somehow and presented it in a merged view. That said - it is not possible to edit anything contact-wise in Signal, it always drives you back to the main contact entry (the first screenshot in my question).
I will put it on the shelf with other unsolved mysteries in my 25 years career in IT.