If you can't get X11 or Wayland GUI Linux apps to start anymore on Chrome OS, try the following.
In the Terminal app, this will show the status of your systemd user services/units:
systemctl --user
If [email protected] and [email protected] show a failed status, the following worked for me:
sudo ln -s /opt/google/cros-containers/bin/sommelier.elf /usr/bin/