You can make use of these options either by invoking zellij with zellij options [OPTION] or binding them in the configuration file.

Eg. zellij options --simplified-ui is equivalent to simplified_ui: true in the config file.

default-modedefault_modenormalThe first mode on startup.
simplified-uisimplified_uifalseRequest the Plugins to use a more compatible ui.
themethemedefaultSwitch to a theme configured under the themes section.