Obviously I can read books, do personal projects, etc to learn the subject matter, but I don't know how to actually get my resume looked at. As you get more experienced I'm not sure that personal projects will really stand out unless they're really built out/significant. Is contributing to open source the best way to show that you can do work on real codebases? I don't want to spend the next year building out some toy project only for it to not be seen because no one will look at it.

Side question: how do you actually find these jobs? There are some companies that obviously have them, but it's surprisingly hard to dig them out. "Systems engineer" brings up tons of unrelated stuff. Searching by language doesn't get super far either, because c++/rust are used more widely than just systems (and searching for the single character "c" has obvious issues).