well, the code works great but now I got 2 private forums (10 and 11), and i want that forum 11 stay hidden for not registered users and forum 10 to be visible but not accessible.
is that possible?

I suppose the forum is not visible if it's just defined in $clForums array, by default.

You may also check this thread:

Showing closed forums publically

No, the code works fine.

But my question is:

i got 5 forums and 2 private forums. (for example forums 6 i 7 are private forums).
I want forum 6 to be visible but not accessible (i get that when i
paste $show=TRUE; before the condition if($show){ and that works fine.

But i want forum 7 to stay hidden for not registered users.

I hope that you understand what I'm trying to say :)

But i want forum 7 to stay hidden for not registered users.

Did you try this: https://www.minibb.com/forums/7_2865_0.html

thank you!
this is the code i wanted and it works great!
https://www.minibb.com/forums/7_2865_1.html#msg23379