Learn reading code (by reading code…) of high quality open source projects. It helps getting new concepts and actual creative coding patterns for concrete problems (unlike learning all these “design patterns” in books that IMHO are often just boilerplate generation (hard take I know…)).
Start coding (open source) projects, especially challenging ones, and keep pushing your limits, by trying to learn new smart things, how to achieve problem X. I stagnated in my workplace for quite some time, got unhappy (around COVID), scaled down working hours significantly (I have quite a spartan life, so I can fortunately afford it), and am coding a lot more open source since then. I think I almost learned more in the last 2-3 years until at least to the years of university (quite some time ago), maybe even more than in university, and have a lot more fun while coding. I think going in depth with a programming language comes automatically, when the project is fancy enough, I learned a lot of limitations of Rust (and thus basically reached the deepest level of (parts of) the language) while designing smart APIs.
Yep this sums up my experience quite well too.
I want to emphasize two things here: