Hardware and software keys

I know it may be stupid but I want to test something. So is it possible to get hardware and on screen buttons working at the same time on rom like cyanogenmod 12.1 where is no option in settings to choose that? I found some old forum thread where was told to edit build.prop file but I tried it and I got only lights on hardware keys but buttons doesnt work.

Hardware root

Evening Guys,

I was wondering if the hardware root was usable on every firmware even : 51.1.6.3_516012020

Thanks in advance