[WhoCares]

https://www.learncpp.com/

or read the primer books by Bjarne Stroustrup:
https://www.stroustrup.com/

C++ contains a lot of features which can be considered deprecated or only for compatibility with old code base(pure C or before modern c++)

such as:

"enum class" vs. "enum",
"std::variant" vs. "union",

IMHO, 3 of the most important concepts(philosophy) of C++:
type-safe(through compile-time check)
exception-safe (through RAII and unwinding)
compile-time optimization(through template metaprogramming, constexpr/consteval, static reflection)