Learning more about music theory is the quickest if not the only way to reliably become a better composer. Yes, you can just write stuff that "sounds good", and it probably will! But you simply will not reach your full potential as a composer by just trial and error at a piano without any direction. If nothing else, it is apparent that someone doesn't know music theory when their pieces or cues have no sense of structure or macro planning. There is no special sauce or eureka moment where you'll suddenly be able to write like Williams or Steiner or Korngold etc. It's practice and dedication, just like practicing an instrument, or becoming a surgeon, or mastering a martial art. Nobody is born a legend. If you want to be one, you have to study and practice like one.
I say this as someone who thought I just had a good enough ear to write great stuff. To be honest, if I had just started composing without any theory knowledge, I'd probably get away with it, especially these days. I played in a lot of musical things in and out of school in high school and did arrangements and small composition, and then went for a music degree and learned very quickly just how big of a difference proper music theory can teach you about the composing process. For the first two years of undergrad I and all the other music students had to take 2 years of theory/history. Literally every day, the things our professors taught us completely changed some aspect of my composing process, whether it was opening my eyes to new ways of harmonization, to new pieces, composers, and genres to listen to and study, to something as simple as an instrumentation choice. I cannot stress enough how happy I am I took those classes, and I can't say I'd be a composer doing the great things I am these days were it not for the stuff I learned in those two years.
Knowing more about music theory changes the way you experience music. It makes it much much easier to find out why a particular song, whether it's a movement from a bruckner symphony, or a billie eilish tune, works the way it does, and that's something every composer should be able to do in order to hone their craft. It also makes it a lot faster and easier to try and decipher what a client wants when they say "more epic" or "more sad" or give you a temp track and tell you they want the same "feel".
TL;DR: You are not going to become the next John Williams, Korngold, Rosza, etc. By following your ears alone. Nobody is that good. Take music theory classes, read a book, study some scores, do some counterpoint excercises. Listen actively to music. Instead of just thinking "that song makes me feel sad :(", figure out why. How can you capture the energy that song was able to transfer to you? How can I implement that energy into my own sound and identity?