Does anyone have examples of well-written modern C++ code out there? I used to consider myself a C++ expert like circa 2011 but it's advanced to so quickly that it's almost like a foreign language to me... (though I have tried to keep up a bit... but it's hard without nontrivial examples)

I don't really have experience to properly judge it myself, but Jason Turner is highly regarded in this area and references his ChaiScript project a lot in his talks (which are worth looking up on YouTube): https://github.com/ChaiScript/ChaiScript