I’m not 100% sure how Apple Books works, but you can upload books to kindle. If you google “send to kindle” you can drop any document you want access to on your kindle. I think your kindle also has an email and if you send a document to that email, it’ll upload onto your account but I’m less familiar with that
oh yeah no it’s not like a common thing. but it’s still something to be aware of. I personally don’t like the idea of spending my hard earned money on products I don’t actually own and it’s something I’m growing more wary of as I’m seeing how the US’s political climate is changing. If this continues, I really don’t put it past Amazon to censor or delete books from marginalized authors to satisfy book banners and bigots