I think you are confusing Amazon products.
The Amazon Kindle line (with eInk display) just act as book reading, Ereader for library books, reader for eMagazines or [some Kindles] as note taking devices. There really is Not any access to any other apps using a Kindle. Although using 3rd party software (e.g.,
https://calibre-ebook.com/) on a computer, one can use Kindle with ebooks from Apple Books or Barnes & Noble.
There is a different line of Amazon tablets (Fire Tablets) that are closer to traditional Android tablets but with LED display that can run Android Apps [Although the Amazon Fire Tablets come locked to the Amazon Store, they can be tweaked to access the Google Store]. They are primarily very low cost devices oriented to media consumption, email, web browsing and simple games.