That is right. Those are set when a desktop is installed via dietpi-software but not for manual desktop installs and not for X11 installs. Probably we should instead set those defaults whenever X11 is installed.
Those are present here without an X11 reinstall, when trying with minimal/core install. Also, the cinnamon-core package install does not replace/uninstall anything of the previous X11 install, so the reinstall should be a no-op doing exactly nothing. Tested again with cinnamon-desktop-environment which has the same result. Those shutdown options are generally provided by the upower package. While this is not installed with X11, it is a dependency of cinnamon-core
Tested on Bullseye x86_64 VM. Can you reproduce this on RPi only?
Until we found the reason and proper solution for this, I suggest to adjust the blog post to not first install X11, then the desktop, then reinstall X11, but instead install desktop, then install X11, just to avoid the same step two times 
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