I would probably start with JavaScript and TypeScript, because you can build so many things with them. You can be very productive and employable with them. But

I would probably start with JavaScript and TypeScript, because you can build so many things with them. You can be very productive and employable with them. But then I would probably want to dig deeper, and start learning C, Zig, with a side order of WASM, along with data structures and algorithms, operating systems, processor architectures, memory hierarchy, network layers and protocols and all that. I would still keep mastering my web knowledge though, eventually including Remix, Qwik and similar JavaScript frameworks and the paradigms they introduce. I wouldn't miss Martin Klepmann's Designing Data-Intensive Applications book either.