I've started avoiding the Kindle App, too much control of Ebook market by Amazon.

As an alternative, I use Ebooks.com and others, buy EPUBs and then remove the DRM (legally) and put the books into my Calibre Library. I have a Boox ereader and have large chunk of my library loaded. I also have the Kindle app on there for my older kindle books.

It's a little faffy but I truly own my books forever. Amazon can't decide to just delete them or if I get locked out of my Amazon account I don't lose everything; this has happened to multiple people! There are stories of people crossing borders and being locked out of their accounts due to falling foul of the DRM rules.