Skill development plan for junior C++?

Question

C++ / C#

Hello everybody.
Initial data: several years of work as a software engineer in a research institute.
What I had to work with:
C (quite a lot, but without any complicated things in the form of microcontroller / assembler programming),
C ++ (mainly used to build small / medium software models for analysis / experiments. No innovations and some complicated language things, a bit of STL, for C++ development was done in embarcadero studio... ), little things working with Lua, using CUDA.
I am planning to change jobs. There are a lot of uninteresting / tedious tasks, reports, revisions, etc., I will not go into depth. As you can see the skills are small. Now I want to quit my job, take a break, devote a few months to improving my skills and look for a job in Moscow.
The question is what to study, what experience to gain? The first thing I think about is sql, working with the database. If you continue to work with C ++, then QT. Maybe you should look towards C#, Java? There are many more vacancies.
It would also be nice if good courses / books / articles on these things were advised.
Thank you.

Answer 1

Still, if you decide to switch to another language, I will give you my (actually not mine) plan for learning the language. If you do not dare, then look at what you still do not know how:

1. Information about the language: paradigms, typification, scopes.
   
2. Variables, data types.
   
3. Structures, classes.
   
4. Cycles, branching, choice, functions.
   
5. Object-oriented programming.
   
6. Technologies: working with files, multithreading, asynchrony, graphics, sockets, databases, web, working with XML