Apple Books and reading with the Polaris Mini

Hi everyone,
two days ago, for the first time I entered into the app Books, I mean de app Books from Apple which is contained in the iphone and in the Mac device, and I fond a lot of books in which I would be very inerested and which I would buy, above all, books in foreign languages, as english, and others. However I have a problem. In order to read in a foreign language, and in eveyr language in general, I need a Braille Display, and unfortunatelly, everyone told me that if we buy a book from apple books, it is not possible to transfer them somewhere and so, it is not possible to transfer them into the Polaris Mini (this is the Braille Display that I decided to buy and that I will buy in next weeks). Of course, I could read books connecting hte Braille display with the Iphone or the Mac, but this is not a good solution, because it spends a lot of batery, and it is not confortable for me, so, I prefer to read them directly into the Braille Display. Do you know a solution to reach it?, As a suggestion, I think that Apple should and could creat e a sytem in which each Apple user could register anyway only an external devide in order to be sure that people don't copy the books, but the fact to be able to transfer the books into Braille Display I think really very important, abouve all, if we have to read in a foreign language.
In case this wouldn't e possible, I wonder me if there is another solution, perhpas through Kindle app, for example, which I could down load directly into the polaris, but a friend of me told me that KIndle at least for Iphone, is not very accessible, someone has experience about it and could give me some idea or suggestion about this matter?.
It's really a pitty because, as I said, there are in Apple Books a lot of books that I would buy to read them in this suummer.
Many thanks in advance and good holidays to everone.
Maria