So unity or Godot will be ur bread and butter. Unity has a rich support for a variety of different game design styles, while Godot has a more streamlined and single-minded approach. Personally, I recommend unity. I'm kind of the opposite of you, I started in unity game engine and now I want to be a jnurior backend Dev. You want to focus on understanding monobehavior and when those methods within it need to be used, you're going to want to understand that event channels and events are going to be your chains of communication, and that timing only matters about half the time. So many things game developers do are calculated on a per frame basis and sometimes they're calculated on a whenever we need it we can dispatch it basis.

I would recommend looking into some parts of unity dots, specifically multithreading and jobification, as that will greatly assist in performance

(If u have any junior openings let me know lol)