Beyond discussing what Modern C++ actually means, Andrei Alexandrescu book, C++11, C++14, C++17, C++20, C++23, this only goes to show how "modern" is the C++ code from companies that should know better as WG21 members, and C++ compiler vendors.
Let alone those that aren't neither WG21 members, nor C++ compiler vendors.
Let alone those that aren't neither WG21 members, nor C++ compiler vendors.