I've been a reader for more than 40 years.
Since I bought my Kindle Fire (Wi-Fi) I've bought and read over 50 new books, mainly fiction (SF & Fantasy) but also Mil History and I've made a start on clearing the house of forty years of accumulated paperbacks. There are some books which will NEVER be donated to charity - good bindings, some with sentimental values, some rarities but my entertainment books can all go electronic & be ephemeral.
My practice was always to use the >Manage Your Kindle>Download & Transfer by USB cable option which has given the chance to archive the *.azw and *.azw3 files. As well as being saved on my PC (1TB external drive) I've backed the archive up on a 32Gb USB thumb drive (Backup protocol - Father, Son, Grandfather), so the possibility of Amazon deleting my books doesn't exist.
Other Kindle users, especially those who don't have a country-specific Amazon store, try the Calibre software which lets you source e-books from ANY location in any (of a wide range of) format, convert them to *azw3 format and read them on your Kindle. There are a lot of e-books which are legal and free. It's also a good library management tool. You can assign series references to your books (and lots of other stuff)
However, I seem to have fallen foul of a known major Kindle problem (at least - there are a lot of You Tube videos about doing the hardware fix) which is the vulnerable mini-USB charging port. It's wobbling and needs a lot of care in manipulating the cable in the port in order to get it to charge again.
I don't have the tools or fine soldering skills to do the repair myself and can't seem to find anybody here in Oz who would do the repair.
I may have to buy a new Kindle.