You might need to update LibreOffice ...
Mine: /usr/bin/soffice --version
shows: LibreOffice 18.104.22.168 30(Build:1)
You didn't shared back this info:
/sbin/service unoconv status
Should show a green character then:
● unoconv.service - Unoconv listener for document conversions
Is it active?
If you have no service listening then it also won't work!
If you un-install unoconv (could do that simply by removing the python script in /usr/bin file is unovonv ... but IF you do then it's broken for sure!
Only alternative would be Google conversions. And you are 'worried' about that as well. Soooo ... I can't make any calls for you. You decide ... it's why you make the 'big bucks', right?
and if you are gonna raise an issue of privacy using Google, then guess you'll have to find a way to make unoconv work!
My advice ... leave unoconv installed and upgrade LibreOffice.
Both unoconv and Google (once set up) can co-exist on server. In Moodle admin interface, admin user chooses which the system is to use. The other then is dormant for all practical purposes. Never called by Moodle code at least!
Yes, unoconv listener has been problematic from time to time ... and needed restarting to properly function.
Use whatever works on your system and has the least need for
troubleshooting ... hmmmm ... does anyone have a moodle server that
*never* has issues from time to time? .... in a 'perfect' world! Hmmmm ... is there such a thing!