>> > I am trying to completely disable the zsh completion system.
>>
>> Does this do what you want?
>>
>>     bindkey -r '^I'
>
> No, I have already unbinding Ctrl+I. It is also not helping.

The bindkey command I posted above makes TAB do nothing.

  % ls<TAB>

Nothing happens.

If this isn't what you are looking for, please explain what you want to achieve.

Roman.