I have heard it so many times from people that learning philosophy and science will be dangerous for our faith. They told me that some Islam women started to take off their scarves after going to philosophic class. I even heard a professor said that his students would lose their faith in free will after learning from his class. I don't know about others or whether those cases really had a correlation to a faith erosion, but for me, the more I learned about those things, the more I feel the greatness of God and the more I feel that everything is made with a great balance. I don't think that those concepts contradict to Islamic teachings, particularly about essentialism and existentialism.
First of all, let's talk about what are actually essentialism and existentialism. If you are into Plato or Aristotle, you are maybe an essentialist since they supported this idea, that everything has their own essence. This notion means that every single thing and what will happen to all these things are predetermined. For example, if in the future I will become a great researcher, it is all because I have the essence of a great researcher from the very beginning, and it's not, based on essentialism idea, that I want to be a great researcher. In the other hand, if you are into Sartre, you are maybe into existentialism. According to Sartre, every individual is free and can determine what they become in the future. If you are a waitress, it is because you wanted to be a waitress. You can be everything that you want to. Here, humans are viewed as having free wills.
Alright, I will give you more example for each of those constructs. Do you believe that everyone has a passion and/or talent? Okay, maybe you are an essentialist. That's one example. Then, if you dive into molecular genetics, then maybe you have this understanding that you have no single control to your own selves. Your traits have been defined by genetic inheritance; they are already written to your DNAs. Also, whether particular DNAs in your body triggered or not and functioning or not, they are defined by the environments around you that you capture by your senses. In mouses, for example, based on a research, the more their moms licked them when they were just mice, the more they have the calmness in their adulthood.
So, how does Islam view this topic? As far as I know, there are three ways existing. Jabariyah people hold the tenet that everything is already written previously, the absolute fatalist. Based on this idealism, humans are not free and cannot decide anything that will happen to their own lives. In contrast, there are Qadariyah people that view humans as having free wills. Here, we can map that the Jabariyah people are essentialists. Meanwhile, the Qadariyah people are the existentialists. What is the third one? The third one believes that life is a combination of fates and free wills, and this one is the view that I hold. I believe that things have been written as fates, yet humans still are given the ability to change some of those fates, with decrees from Allah. Actually, this third notion is also supported by a lecture from Bayyinah Institute. You can view the lecture here. The reason why I like this idea is that there are ayahs in the Qur'an that mention about fates and also ayahs that imply that humans can change their fates (e.g. Surah Ar-Ra'd: 11). There are even sequential ayahs that imply about it.
وَنَفْسٍ وَمَا سَوَّاهَا - 91:7 (And [by] the soul and He who proportioned it)
فَأَلْهَمَهَا فُجُورَهَا وَتَقْوَاهَا - 91:8 (And inspired it [with discernment of] its wickedness and its righteousness,)
قَدْ أَفْلَحَ مَن زَكَّاهَا - 91:9 (He has succeeded who purifies it,)
وَقَدْ خَابَ مَن دَسَّاهَا - 91:10 (And he has failed who instills it [with corruption].)
In my opinion, I feel some benefits of going into this belief. First, I can separate the things that I can control and the things that I cannot. With this, I can just focus on the things that I can change and hence it will reduce the stress of my life. This is like Marcus Aurelius's Stoicism view, right? (Yes, I like some ideas from Stoicism but not all of them. Like the idea that it is OK to do suicide, I don't buy it. Just no!) The second benefit is that...it is actually romantics, Lol! For example, your soulmate's name has been written as fate and it's like an adventure finding the one that is meant to you. It is just mumumumumumumumumu.