That’s one of the reasons I jailbreaked my phone, to be able to control which app can access which data and when.

your answer doesn’t make any sense in this context. this is a standard whatsapp feature that can not be turned off. you can disable networking and open whatsapp and that flag will not be sent, but also your conversations won’t get updated. jailbreaking doesn’t change any of this.

If you have root you could decrypt the traffic on the fly, and block any data that is not necessary for basic functionality. Maybe even run squid locally, and configure it there. I doubt that's what they meant, and it would take a bit of reverse engineering, but would be kind of fun.

https://watusi.fouadraheb.com/ Check the privacy features.