Small update: I found out that the leverage is applied automatically and one cannot change this manually on IB.
This is what I misunderstood how trading on margin works. I was used to being able to manually set the leverage as it is possible with the CFD broker etoro.
So i didn't know that other brokers are handling this differently.
E.g. I have another broker account (tastytrade) there margin trading gets suspended, if the cash falls under a minimum margin amount (2500 in my case). In that case trading is effectively done 'by cash'.
So little note for myself: Always check the broker

Probably this info is well known for most of you. But maybe it helps others that are new to active trading like my humble self.

Greetings
Trail