> You can now use the same WhatsApp account on multiple devices at the same time, using your primary phone to link up to four devices. You’ll need to log in to WhatsApp on your primary phone every 14 days to keep linked devices connected to your WhatsApp account.

ref: https://faq.whatsapp.com/1317564962315842/?cms_platform=ipho...

> Use WhatsApp on your computer even when your phone is off.

ref: https://faq.whatsapp.com/378279804439436/?helpref=faq_conten...

Yes, and it works, as it has for the past few years.

So I don't need my primary device any more? I can just shut that phone down forever?

No, I think you need it to be online once every 30 days or so. That's a much weaker requirement than what you were disputing, though.