I had found the 2nd option (Advanced Permissions for Registered Users), but I missed the 1st (Enable dice). I had only selected the top forum in order to include all subforums, but there is no Enable dice option there. Thanks to you I learned that I had to select every single forum separately for the option to show up.
I now see the Dice rolls option when posting in a thread and it works. Do I always have to click this in order to roll a dice? I tried manually entering something like
[roll=1]1d6[/roll]in my post, but it will just show up like this: