Why doesn't the okular bundle support epub?

according to https://okular.kde.org/formats/ , okular supports epub. so why when i try to open an epub with okular, do i get the following message: org.kde.okular.core: No plugin for mimetype '"application/epub+zip"'.
in the gui:
Could not open file:///home/glanard/Desktop/books/python-3.9.7-docs.epub.
Can not find a plugin which is able to handle the document being passed.