Ok, CentOS 8 from a VB image from osboxes ... installed just today.
Moodle 3.9.x installed via git just today.
Unoconv successfully installed and converted docx -> PDF both scripts provided you for testing and via 3.9 after setting up.
Installed python3 ... in unoconv had to change first line - the shebang! line
because I had installed python3 - in CentOS 8 repos there are python2 and python3
LibreOffice I tried to install minimal ...
dnf install libreoffice-data.noarch \
but it also installed libraries ... bunch of space.
Acquired the uno_ghost test files from sos.sosoftexas.org.
Ran the bench scripts contained there in.
What that outputs might help you trouble shoot.
Script did complete successfully - clip below ...
Selected output format: Portable Document Format [.pdf]
Selected office filter: writer_pdf_Export
Used doctype: document
Output file: file:///var/www/html/uno_go_test/hp-unoconvtest.pdf
DEBUG: Terminating LibreOffice instance.
DEBUG: Waiting for LibreOffice instance to exit.
[root@osboxes uno_go_test]# ls -l hp-unoconvtest.pdf
-rw-r--r--. 1 root root 13070 Jun 19 20:10 hp-unoconvtest.pdf
Set up the listener as per docs:
Stepped through Admin interface set up for document conversions
and the path to unoconv ... test path OK
And downloaded the converted.pdf test file.
So ... doable for sure.