CPU speed control and power consumption on /e/

Hi, I’ve just bought an S9 and installed /e/.
I would like to slow down the CPU speed in order to decrease the power consuption and consequently increase duration of use. Should I root the S9 in order to install some specific app (application without any tracking of course), or is it possible to change CPU max and min speed in real time inside /e/ ?

Notice that I use my phone only to make calls and writing sms, I absolutely don’t care about video, streaming and any power CPU consumming applications. I use my computer for that. My old Nokia 302 phone juste died, battery had worked like a charm for 10 years and even few days ago this old phone was able to keep working without charging for 5 days with 1 or 2 hours of conversation ! USB connector broke so it was time to change and I was forced to get a smartphone for several reasons, including european banks pressure (you cannot pay and verify the payment without a smartphone now, it’s the end of sms verifications in France). So if I had to chose a mobile phone, I chosed one with /e/ for privacy reasons, because I hate google and all trackers.

Anyway, if you could adviced me how to change CPU speed, it would be very appreciated.

Thanks in advance.

I recommend to try the implemented energy saving feature or Kernel Adiutor

I Installed it, but it says “No root”.
What I am supposed to do root the phone ?

If you want to use it, yes.

You probably read too fast my question ! I asked how to root the phone ?..
I have no experience at all with those things.