Adding additional PPA's fails with Error: must run as a priviledged user

Trying to add a PPA via the GUI in Libertine settings silently fails. Trying it in the terminal with libertine-container-manager -a add -n ppa:team-xbmc/ppa fails with error message Error: must run as a priviledged user

Same here on focal (Ubuntu 20.04).

If I try to run it as sudo, I get this error message:

phablet@ubuntu-phablet:~$ libertine-container-manager exec -c "sudo add-apt-repository ppa:apandada1/libhandy-1"
sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set

Also the installation of local packages, as explained in the user guide, will fail due to missing super user rights:

phablet@ubuntu-phablet:~/$ libertine-container-manager exec -c "dpkg -i /root/libhandy-1-0_1.4.0-0build1~ubuntu2004_arm64.deb"
dpkg: error: requested operation requires superuser privilege

And again, if I try it with sudo, I get the same error message:

phablet@ubuntu-phablet:~/$ libertine-container-manager exec -c "sudo dpkg -i /root/libhandy-1-0_1.4.0-0build1~ubuntu2004_arm64.deb"
sudo: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set

If you install the Libertine Tweak Tool, you can use the lirsh command to get a root shell in the libertine container. Once you get root access, you can add PPA's and install packages as normal in ubuntu.