I am posting a solution information to anyone installing unoconv with LibraOffice, and getting the same error message.
(This is not a direct solution to the above issue)
I had similar error message after trying to test the unoconv service I just installed on a RedHat 7.9 server.
I installed LibraOffice 7.3 directly from RPM packages and not used OS yum packages (ver 5.3)
So the libreoffice-pyuno was not found (bind) to the unoconv, and that is way I got a similar error to the one you got.
You will have to download find_uno.py from here to fix this: https://github.com/unoconv/unoconv#installing-unoconv
(This is not a direct solution to the above issue)
I had similar error message after trying to test the unoconv service I just installed on a RedHat 7.9 server.
I installed LibraOffice 7.3 directly from RPM packages and not used OS yum packages (ver 5.3)
So the libreoffice-pyuno was not found (bind) to the unoconv, and that is way I got a similar error to the one you got.
You will have to download find_uno.py from here to fix this: https://github.com/unoconv/unoconv#installing-unoconv