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.