https://cppbyexample.com/
https://hackingcpp.com/
https://www.learncpp.com/
https://github.com/AnthonyCalandra/modern-cpp-features
https://cppinsights.io/ it's a must so you can investigate what gets generated by templates behind the scenes.
http://eel.is/c++draft/ bookmark this, you will need it!
Enjoy!