10 years as a developer, how to double down and improve?

Hey HN,

I've spent 10 years working as a software engineer now, and I can't help but feel that I'm very shallow in almost everything that I do. I've worked for small early-stage startups, and a FAANG and now am at a midsize corporation. Happy with my job but I want to double down on being a developer.

I want to build impressive things. I want to try my hand at a text editor from scratch. I want to build an HTTPS proxy that works at the byte level, opening sockets and applying encryption. I want to do all these things and whenever I start these projects I realize that my only skill that I have is building applications on top of modern frameworks and libraries.

I have no understanding of the fundamentals, don't know when to reach for more powerful data structures, algorithms, etc. I'd like to have an understanding but I've just never built it.

I've fallen prey in the past to the "shiny new thing" syndrome and now am doubling down on a small set of languages to "Get Stuff Done." How can I double down on being a developer? How do you improve on technical skills 10 years into your career? It's been ages since I've had a mentor to look after me and help me to get better at what I'm doing. What do you all do to keep building relevant skills and keep improving?

I've spent plenty of time improving soft skills as well, but really love the technical side.

Thanks in advance for any help/responses.