Question: Correct way to set the Preferred domain in Search Console?

The infamous google search console question.
I need to set a preferred domain and to be honest, I don't think i've ever thought about it until I found
duplicate indexed urls for one of my websites that let me to check another.

Maybe someone can give me some guidance here =)

The domain I want to set as preferred is the non-www version. I've added both non-www version and www to search console

This is what I set for the non-www (I want this to be the preferred).

Preferred domain

Don't set a preferred domain
Display URLs as www . domain . com
--> Display URLs as domain . com


This is what I selected for the www (this is my non-prefefred)

Don't set a preferred domain
Display URLs as www . domain . com
--> Display URLs as domain . com

Question:
Is this the correct way to select the preferred domain or should the www (the non-preferred) be set to "Don't set a preferred domain".

Thanks for any input