I had this message after I removed libfreecad-python2-0.17 which was preventing my updated freecad from running properly
I then did apt-get install freecad-python3 I got the message Setting up python3-pyside2.qtopengl (5.11.2-3) ... Setting up libfreecad-python3-0.18 (0.18~pre1+dfsg1-4) ... Setting up python3-pivy (0.6.4-1) ... Setting up freecad-python3 (0.18~pre1+dfsg1-4) ... update-alternatives: warning: forcing reinstallation of alternative /usr/lib/freecad/bin/freecad-python2 because link group freecad is broken but my system now seems to be working - I suggest trying doing an update-alternatives to force freecad-python2 to be used properly