For iOS there’s something called KyBook which reads that opds link and shows a list of books with cover art, book name, author and tags pertaining to the books subject matter. It does not allow one to search the opds library in anyway. I was able to download a book using the app, and from within the app move the book to iCloud. From within the Files app I found the KyBook folder, selected the book and using share opened it with iBooks and it is now in my iBooks collection. I found the app here https://www.maketecheasier.com/best-ebook-reader-ios/