> [reformatted]
>
> (zshrc
>  (list (computed-file
>         "zshrc"
>         #~(begin
>             (reduce string-append ""
>                     (list "bindkey -e\n"
>                           (format #f "source ~s/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh\n"
>                                   #$zsh-syntax-highlighting)
>                           "eval \"$(direnv hook zsh)\"\n"
>                           "eval \"$(zoxide init zsh)\"\n"))))))

The gexp passed to computed-file should produce a file when built
(evaluated)[1]. Your gexp doesn't create any files or directories, it just
evaluates to a string. Try using mixed-text-file[2] instead.

It is not relevant to this error, but I think your path to
zsh-syntax-highlighting.zsh is wrong. In my configuration it is
"/share/zsh/plugins/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh".

[1]: https://guix.gnu.org/manual/devel/en/guix.html#index-computed_002dfile
[2]: https://guix.gnu.org/manual/devel/en/guix.html#index-mixed_002dtext_002dfile

> And I receive following error:
> 
> ------------------------------------------
> $ guix time-machine -C ./channels.scm -- home reconfigure config.scm
> guix home: error: reference to invalid output 'out' of derivation '/gnu/store/2dqwm651a0p0vqwhpvsy7dn8zvx4n99x-zshrc.drv'
> ------------------------------------------

The error says that the derivation (created by computed-file) does not
produce an output named out (because the gexp doesn't produce any
outputs).