Need tips on improving/learning advance CPP

Hi folks,

(Please remove this if this is the wrong sub for this question)

I’m trying to start a career in CPP and parallel programming – I’ve been a Java/Python/JS web developer mostly for the past 3-4 years. Now I’ve got into C++ and parallel programming (OpenMP, MPI, SYCL ..etc) recently with a degree I completed, I’ve become really passionate on learning and practicing low level programming. But I’m finding it difficult to get into a proper C++ job and looking to shape up my skills and become confident. Appreciate if I could get some tips from you all on starting/doing some side projects before applying for jobs again. By “side”, I mean to not involve 24/7 because atm I’m working on a PHP web application part-time so I can spend 3-4 days a week for C++ development. Special tips on mastering >= C++17 also welcome as I’m somewhat comfortable up-to C++14. Anything from new project/header library ideas to contributing to existing projects is welcome.

P.S. I’ve had a look on open-source C++ projects but I couldn’t find any simpler ones to start with.

TL;DR Ideas needed on a beginner C++ projects/libraries with special focus on parallel programming to develop industry-focused skills and in-depth understanding.