It sounds like you’re in the right area by focusing on C. Have you got a GitHub profile? I’d start looking for open source projects in that space and get involved. Many of them have beginner bugs and tasks. Some projects are better than others at welcoming juniors, so check their readme to see if they have any advice.

If you’re interested in low-level languages like C and C++, I would take a look at Rust. It’s another performance-focused language that complies to assembler like C, but includes some clever design principles to prevent a lot of common C/C++ bugs from being possible at all. Even if you don’t end up using it much, it’s quite interesting to see a different way of thinking about things to achieve a similar output.

Beyond that, I’d say you need to think about the job opportunities you’re interested in and learn what tech they use.

Especially considering it scales by adjusting accuracy! That makes it very adaptable so it could be used everywhere from microcontrollers through to Google data servers.