With a jailbroken kindle you can install the BBB (Block Big Brother) filter on the firewall (it's running linux under the hood after all):

https://www.mobileread.com/forums/showthread.php?p=2425330

Alternatively like me you can just remove the 3g modem in it's entirety:

https://peekread.info/tech/20210120-removing-3g-modem-from-a...

what happens when you buy Kindle in EU, I would think when you first turn it on they would have to ask if you want to be tracked and if not would have to fuck off.

That's a good question I couldn't find anything in my cursory searches. Knowing Amazon because all the focus has been on Web browsers and cookies there might not be much available on the ebook front atm.

Kindle with ads has been observed to, after a couple alerts that it’s been offline for too long, just ignore airplane mode at some point.

I have a wifi only model that has never seen a wifi password, and haven’t noticed this.

What’s the symptom?

Can confirm. Happened with me couple times. It would just go off the airplane more altogether.

Besides, "airplane" mode is just an icon on the screen. If it has WiFi with a known password (or without one) within reach there's really no way of knowing if it's phoning home.

Amazon never denied the fact that they use their devices to collect data. That's why they are (relatively) cheap. Kindle, Echo, Fire TV - they are al presumed to provide data to Amazon on customer's preferences allowing for better ad targeting etc. If this data can be sold to third parties, even better, more revenue. This is not illegal and I'm not even sure it's unethical, as long as the buyers are aware of the deal.

I keep it 100% in airplane mode and use calibre to manage my library. So far it’s been a pleasure, reliable and predictable.