After some investigation I found the command “apt-mark”.
Connected to FBX by ssh as admin and issued apt-mark showhold:
**********@freedombox:~$ apt-mark showhold
freedombox
Would it be possible and safe!! to do “apt-mark unhold freedombox” and afterwards perform a manual upgrade in plinth > system > upgrades?
Since I don’t have a clue why the package is being kept back I’m not sure whether this procedure is a good idea.