How to learn building C# Unity project at professional level

I want to level up my skills of building a Unity project using C#, I'd love to better organize my classes, use more design patterns than just using a lot of singletons and creating a lot of managers, maybe use some event driven design, I want to be able to write project that scales from beginning instead of refactoring over and over, I also want to write projects that don't have a lot of performance red flags.

I have CS background, I work in IT company, I understand C# syntax, but I don't have a game code base I can read and learn from. As a hobbyist who only learns making game in the evenings and weekends, how do I quickly get to the professional level so that I can make games that ship. I've been following some online tutorials like Brackeys but they typically teach you how to implement a specific mechanism rather than help you build a maintainable project.

More specifically:

1. Is there good tutorial or book that teaches design pattern, scaling, with good examples, in a cover-all manner?
2. Where do I find good projects I can read and learn/mimic if I don't work in a game company.
3. How did you become a decent game programmer? What steps or stages did you go through?

Thanks in advance!