I do have a book extension is .jarirreader from https://jarirreader.com/
Images contains the cover / index has Json format / Text has chapters with HTML extension.
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It's most likely a custom format with DRMed and/or obfuscated files. Try opening the files in the text folder with a web browser. If you can read them in a browser you can re-assemble them to a book with an epub editor.