Unable to read Books purchased on iPhone 7 on my more recent Apple devices

How to save/transfer/convert purchased downloaded books from Apple iBooks or AppleBooks on iPhone 7 Plus that cannot be opened in Books on Mac Pro 2013 or 24 inch iMac 2023 or in iCloud?

Error message: Cannot Open "book name". It is formatted incorrectly, or is not a format that Apple Books can open.

I have a collection of 32 purchased books from Apple that I can read on the iPhone 7 Plus, but cannot read anywhere else. I also have hundreds of PDFs that I saved to iBooks/Books on the iPhone that I am at least able to send elsewhere and open. However, even though the books can be read on the iPhone 7 Plus the device will not last forever, and I do not want to have to repurchase the books which are still available in Books but as a different item.

[Re-Titled by Moderator]