I never found a really good tutorial, I had to use pieces from several, but here some links I used:
What I actually did:
- switch to beta channel
- enable the crostini experimental flag
- Turn on Linux in main settings
After that I could install libreoffice with sudo apt-get install libreoffice.
In order to install the .deb Kolibri package, I had to move the package to the “Linux folder” on the chromebook.
I’m currently running Kolibri on a chromebook that I modified the firmware using this script and then installed GalliumOS on.
Thanks for your help.