Thanks for getting in touch with VolThemes Support.
Sorry for confusion, Rubik theme doesn’t use Customizer for the theme option/settings.
You can find the option through “Appearance >> Customize >> Theme Options“.
The theme option include column settings, slider, Post Meta Settings, Ads, lot of Color setting section, Footer setting, and many more.
We also about to update the theme version soon.
Have a great day and please let us know if we can help with anything else.