Herr are some great resources:

https://en.cppreference.com/w/

https://www.learncpp.com/

https://hackingcpp.com/

Books:

A tour of C++ 2nd Ed by Bjorne Stroustrup covers C++17 and a new version is in the works to cover C++20 and maybe 23.

https://nostarch.com/cppcrashcourse