How to set a person's Key Photo from Photos.app as contact picture in Contacts.app

I have defined a collection of about 300 People in Photos.app. Most of these persons have also a contact entry in Contacts.app. I would like to set the selected face from the Key Photo as contact picture, but I can not get this to work.

There is a similar question from about three months ago ("Sync Photo's People with Contacts"). Old Toad shows (thanks!!) that it should work with newly created Person/People entries. But I have already these 300 People named.

Q: Is there a way to establish a link between Photos and Contacts for existing People/Contact entries?

When I click on the name in the upper left corner of a persons People-page, a dialog pops up that allows to rename the person. There is also a list of contact entries presented (quite long if one has many contacts). However, when I select the Contacts entry fitting to the person, Photos.app crashes. For me, this crash was reproducible although it did not happen each time.

Q2: Does this crash happen only on my Mac (iMac24 with 12.2.1)?