When trying to install zsh got this warning about unmet dependencies:

The following packages have unmet dependencies:
 zsh : Depends: zsh-common (= 5.8-6) but 5.8-6+deb11u1 is to be installed
E: Unable to correct problems, you have held broken packages.

This seems to have originated from an update from the byzantium-security.

unfortunately this update caused some Librem 5/zsh user end up with a non usable shell. Because due to this zsh gets removed when doing a full-upgrade