I can't login in the virtual machine I created

I used this line

./pre-inst-env guix system vm ~/configs/vm-config-desktop.scm \
   --image-size=10GB \
   --expose=$HOME \
   --share=$HOME/tmp=/exchange

In the resulting virtual machine, a graphical login manager pops up

I type "root" as user, empty password
the login starts but then the screen stays black and after a while the
login screen pops up again

This is where I am

$ git describe
v0.13.0-5123-g95bdcc21e

Thanks