How much data collection do Kindles perform?
I can't answer that question exhaustively, but they do have a USB drive mode* and airplane mode, if that's something you care about.
Though the models with ads (basically all of them) do track impressions of all the ad placements around the device, which includes the lockscreen (the display shows ads when it's in sleep mode, both before and after you press the power button), and a banner on the home page.
* - Amazon removed the ability to download books from them to put on your Kindle, but the new ones do still have a USB drive mode
I switched to Kobo when the cable to my Kindle failed and I found out it was proprietary.
I also wanted to switch to epub format.
Worth noting that only the first Kindle, released in 2007, used a proprietary charger, and plenty of devices used proprietary chargers at the time. All of them since have had USB charging.
I don't think that's true, I had several kindles and it was a paper white that looked like it was micro USB, and charged fine on an alternate cable, but would not do direct USB connection on anything but the kindles own cable.
I'm pretty sure that that's incorrect. I worked at Amazon, on Kindles, and we used retail units with whatever random USB cables we could scrounge up, on all of the various Kindles (fire and eink). I also can't find anything on google mentioning it, and just tested with my own (non-Amazon) cable on my own retail paperwhite from 2015.
You may have just had a cable without functioning data lines.
AFAIK Amazon tracks every single metric they can as a policy. For kindles it’s books you’ve read, how much, when, words you’ve looked up in the dictionary, where you’ve connected from…
For this and other reasons, I have never connected my Kindle to the internet [1]. So it can collect away. It will never be able to transmit the data.
[1] after the very first time when setting up the account
What types of data is available to collect from a Kindle, assuming of course the device is used for nothing but reading ebooks?
IP address and location as you move from place to place (LTE/wifi).
Reading habits and library
Political leanings
Other associated metadata that may do more to link that device to your overall advertising profile and help deanonymize you for other data brokers.
Another commenter lists a few options, but even the most basic of data - what a person chooses to read - is personal and private enough to warrant caring about.