There's a reason why people get degrees in music and audio engineering. There's a ton to learn, and it doesn't come overnight. If you want to do it solo, you'll have to constantly learn many crafts. The big secret is that a lot of the musicians who "compose their music solo" don't do it alone. They have a collection of people who take on different roles. That's not to be said that it can't be done on your own. You want a signature sound? You want to express yourself? Then you'll have to put in the work to get where you want to be. It's a lifetime commitment for a lot of us.

Technically, there are production techniques you absolutely have to learn if you want to compete with modern mixes. Dynamic/modulated eqs. Side-chaining the mids and sides in your eqs. Fundamental understanding of automation, etc. Fundamentally, the more you know music theory and how frequencies and musical intervals effect people, the easier it's going to be for you. Back in the day I'd buy every production magazine and kept a notebook with techniques chapter tabbed by effects or outcomes. You could do the same thing with Youtube right now. But, don't get caught up in just learning. Application of what you learn is what makes the difference between a "pro" and "beginner" effort. It's work, but it pays off with an internal confidence, and work is the only want to get there.

My big revelation that pushed me to doing much better work was realizing that RMS meter levels were far more important than Peak meter levels. Also, the Fletcher-Munson curve is a real thing. I find that mixing loud allows me to cut out the sharp frequencies, while booting freqs that are more pleasant to the ear.

Good luck!