I want to buy open source drm free e-books however I see Kobo that is a Canadian subsidiary owned by a Japanese Company while Apple is American with some operations based in Canada, California is closer to British Columbia however they often use closed standards.
Currently, Apple does not offer any hardware form factor with an e-ink display. If the poster was interested in hardware, that would filter out Apple devices.
I also have a Kindle, PaperWhite 3.
The list is long, in short: Kindle has a closed system. Similar to the reMarkable brand of e-ink devices, they make it hard for you to do anything it was not made for, and to be heavily dependent on their services.
You can still run Doom and other programs on Kindle, but I would not recommend buying it new, nor to someone who does not want the hassle of tweaking it, as there are better options working well out of the box.
In the poster case, converting DRM-free e-books to Amazon’s proprietary format is not always straightforward and can cause severe artifacts in your books. You either need time and patience to tweak the settings of your conversion tool, or install something like KOReader that can read them as-is.
Sorry that initial question was meant to convey that E-ink.
OP appears to either have no E-Ink display experience or that is not a hard requirement.
FWIW, you can use calibre to manage your E-Books. Yes, there are sometimes artificers but IIRC they support mobi too (I apologize if that’s the wrong format I actually haven’t used my kindle in about a year)