Is this a per-contact setting or a "universal" one?
It's a universal setting. You have to enable it per third-party app, though. You get to choose whether you want to see them listed with WhatsApp chats or in a separate folder
Account-wide. Though you can only turn it on in Europe.
Each whatsapp user needs to enable the setting once to allow chats with multiple number of third party users.
It's a universal setting. You have to enable it per third-party app, though. You get to choose whether you want to see them listed with WhatsApp chats or in a separate folder