Question:
Where should I place the difficultyslider while OOO is active?
I played till level 16 with it on 50%, but then it started to get really hard, like insanly hard(yes, I know how OOO work)
so I moved it down to 39% are its much better.
But to get the true or rather default OOO experience where should the slider stand`?

Put the difficulty slider where you want it. This is your game, so let the experience be what is best for you. There is no reason to "tough it out" in this game; if you feel things are getting too hard, don't feel bad about turning the difficulty down.

Adjust it in a way that you find satisfactionary. I have it someting between 35 and 40 and I will not listen if anyone says that I should raise it. It is your game, play it in a way you like it, if it is too hard then lower the slider. No need to think much about it.

50.