I put it into airplane mode years ago, and just never turned wifi on again. I use Calibre to add books to it. (I use a little usb-c to micro usb adapter).
There are places and ways to get books without DRM and still pay the authors. It's a faff first figuring things out, but once you do it a couple of times, and discover the treasure troves of standardebooks.org and the gutenberg.org, it really just becomes routine you don't even have to think much about.
In my experience it's a better device without the internet, no device updates, no weird book updates (books updating is an oddly unsettling concept to me).
Also battery life got way better, I get a few weeks of battery life as long as it's in airplane mode. (Sometimes a couple of months if I'm using it lightly.) Granted I usually leave the backlight off, there's sunlight and lamp light, you don't need backlight.
I've forgotten about it for years at a time, charged it up, and it kept working just fine.
eReaders that are really just eReaders (and not an android device with apps and nonsense) are a rare case of buy it for life devices. The best kind of device. Kinda like a good watch, I now expect an eReader to work for a decade or two. I would also expect battery replacement as a part of long term ownership, though I haven't had to replace my battery yet.
Anyways, you don't need Amazon to enjoy a kindle. Hek, it honestly gets better without Amazon meddling with it at random, and the device phoning home or w/e nonsense background traffic it runs over wifi.
Much love for Calibre!