Audacious won't start, doesn't recognize X display:

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 sommelier@0.service and sommelier-x@0.service show a failed status, the following worked for me:

sudo ln -s /opt/google/cros-containers/bin/sommelier.elf /usr/bin/ systemctl --user restart sommelier@0.service systemctl --user restart sommelier-x@0.service export DISPLAY=:0

Check again to see if those services are started now:

systemctl --user

Hopefully now X/Wayland apps work again.