This answer is based on beeshyams's comment.
Download & install the SA Contacts Lite application; it is available on places where you don't need an account, e.g. via APKPure.com.
Start the app.
3.1 enable Export All Fields.
3.2 Disable Export Photos.
3.3 Enable Merge Duplicates.
Click Export, then Start.
A format selection dialog will come ...
SO, it turns out these contacts were infact imported from a google account I actually deleted about a week ago (20 days for it to get permanently deleted). I looked into my sync settings on my phone and saw how this old gmail adress were still there with sync activated. I had to re-create the google account, and logon to find these contacts in there.
I went under settings>apps ticked show system apps, and searched for 'google'. Found my google contacts sync there. Went through a bunch of relevant sounding system apps that didn't all have the contacts permission, and granted contact permissions. It was to several apps, so no telling which one actually made it work.