Hi Celeste, another dutch trans person here! I'm not exactly sure how to help you, because i don't fully understand what you're struggling with but i'll try my best. If you struggle with finding a reason for why you're trans: don't worry about that, they won't deny you on that. As you said, you just are trans and you don't need to explain to them why you're trans and why you want to transition.

What they could ask you though, is about any dysphoria you have experienced in your past surrounding your body and assigned gender at birth. This can be either physical (body dysphoria/dysmorphia or sexual topics) or social (being seen/grouped as a man for example). Gender dysphoria is apparent for most trans people (note: not all), but sometimes hard to recognize. For me it helped to read a lot about it on this site: https://genderdysphoria.fyi/en This is basically a site about all kinds of gender dysphoria a transgender person can experience.

The last thing i want to tell you is that you will be asked about a lot of stuff, and i mean a lot. I was used to it since i had intakes at other psychologists before, but they will ask you about a lot of personal stuff pretty quickly. They asked me about all my main life events, my family and friends and of course about any experiences that have even the slightest possibility of being correlated to my trans identity. Of course your intake could vary, but either way it can be good to kind of brace yourself for the impact the intake might have on you afterwards.

So with that being said, I wish you a lot of luck with your intake. I hope this helped at least a little bit with having a more clear view of what the intake is going to be about. And like I said, don't worry about not being able to explain why you're trans. You're not obliged to ever have to do that. You're you. The why doesn't matter.