Hi
@Anuk , and welcome to the forum!
You say you can't have fats because of the missing gall bladder. Have you tried or have they told you so?
I had no adverse affects from eating fats after they took out my gall bladder, even without 'slowly introducing' them. I just plunged in with a very fatty meal to see what would happen, and nothing did.
However, official advice is like
@JoKalsbeek says, slowly reintroduce fats as to not upset your innards.
There is no official advice to avoid fats forever because of not having a gall bladder.
I hope this will work for you!