How can I learn modern C++?

Take a look at Jason Turners C++ weekly YouTube Channel https://www.youtube.com/playlist?list=PLs3KjaCtOwSZ2tbuV1hx8Xz-rFZTan2J1[^] The early ones go back to 2016, but if you look through the available videos, you'll see he covers new items in C++17 and C++20. Plus he uses a lot of lambdas, templates, and auto, so it might help you get up to speed with those things too. He also drills down into some nooks and crannies of C++, so its helpful there, too. Viewing his videos led me to some other interesting tools, such as the Compiler Explorer[^]

Go on a course, or get a modern book on the subject: since you are familiar with C++99 you can skim the early stuff that you already know.

Addison Wesley do good ones, as do Wrox and MS Press - but a course is better because if you don't understand something the tutor can rephrase it until you do - but the books are a good method for experienced coders (if you do the exercises, obviously(.

You can see the evolution of C++ here[^], which is a page on the site mentioned in Solution 2. It's my go-to site whenever I need to consult the C++ standard. However, its examples aren't always that great.

As the page indicates, the major releases of C++ have been C++98, C++03, C++11, C++14, C++17, and C++20. If you search on those release names, you should find various online articles that discuss the capabilities that were added in a particular release.