Just bought some books directly from a publisher because they were having a sale. Picked the mobi format to forward to myself so I could forward to my Kindle. Whereupon I got an email from Amazon noting that, by August 2022, mobi will no longer work. Well, it will, just not from Documents (if I want to be able to get ebooks to be deliverable to current devices I own, and any future devices, I needed to get it into my Amazon library, though, for some reason, it always went to Docs instead of books; so anything I bought in the past, that I have in Docs that is in mobi format, will not be sendable from Docs to any future Kindle device I own in the future).
I own, like, a billion mobi format books. In theory any already on my Kindle devices, will still be there and readable after August 1st. In theory. I've seen roll-outs before. There can be issues that don't get fixed.
It's not Amazon cutting off other book sellers from being able to sell books that are readable by Kindles, other formats will either still be supported or will, later, be supported (like epub). So I'd just select epub in future if buy from non-Amazon.
Still. An issue that probably will resolve itself without any problems seen by me, but just more anxiety to be added to my life (if I trip and fall and break my ebook and need to get another (or, like just happened recently, the ebook just stopped working), will my books be there?). Ah. Anxiety. If this was a romance book, anxiety is, apparently, a requirement. So I have anxiety now. I didn't want to be in a romance with Amazon, though.