The jacket plugin is a link to a running jackett instance. Do you have a jackett container running? You need that to link it to. Did you also create the extras script mentioned above? It installs python inside the container, which is used by the plugin. If python is not installed the plugin will not work.
Python is installed. It's now apparently version 3.11.10, where it was 3.11.9 when I originally created that extra script, but I assume that's not the reason for a problem...
I'll look into adding Jackett to the container. (Or is it better to create a separate container?)