Personal Advice

Learn advance versions of C++ (i.e. C++11/14/17) as they covers the gaps & issues we normally face in old C++. Not only this will help you to understand why & how these issues occurred & what measures were taken to prevent them, but it will also make you familiarize with other languages too. Since, at that point of time, not only C++ was getting updated with these new features but also the other languages in a bit different format, but the concepts behind them were similar. Like JavaScript, whose constructs are pretty comlpex, but a person with C++ background will have less difficulty to understand them.

Furthermore, you will be introduced with the concept of Functional Programming, which becomes very helpful in learning other concepts such as Concurrent/Parallel Programming. Moreover, C++11 have introduced Move-Semantics (a.k.a rule of five) which heavily optimizes your code.

So, here is a great article for starters which will give you brief intro about the major differences in advance versions:
C++11 vs C++14 vs C++17

Learning Material

- Learn Advance & Modern C++/C++11 (by BoQian, for exploring deep concepts)

- C++ with CppNuts (by Rupesh Yadav, for advance & specific problems)

- C++ made easy (by The Cherno, for basic & specific problems)

- Learn Complete Basics of C++ (by Programiz, full course-outline)

- C++ Tutorials for Beginners (by CodeWithHarry, in Hindi/Urdu)

- Learn C++ Concepts (by Saurabh Shukla, in Hindi/Urdu)

Reference Material

- Cplusplus: (references - tutorials)

- Cpp Reference

Additional Related Material

- C/C++ Programming Queries & Solutions