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.
xclock
It seems that both services are running on my Lenovo Pyro, but I will make a further check.
sommelier-x@0.service loaded active running X11 sommelier at display 0
sommelier@0.service loaded active running Master sommelier listening on socket wayland-0
Thanks for the hint.