The very first mistake you made was using Unity. Start from scratch. A game loop is really just draw(), update() positions in a loop. Even smaller effects can be done with simple programming. Recently I played around with ChatGPT for some effects for JS game, the results were interesting and very experimental. 3D game is another beast altogether and linear algebra needs to be very solid for that.
Or you can use an engine, like Unity.
Edit: you responded and then deleted a post about "games that don't look like Unity on Unity". Ignoring that the looks of a game usually matter less in the long run than gameplay, a very, very short search shows that Escape from Tarkov[0] is made in Unity.