(In 2077.)

CCF: We can use C++14!!!

Concepts, templated lambdas, std::ranges, std::span, and std::format sound like pretty useful features.

std::midpoint will do away with a lot of midpoint related overflow/underflow issues, which is a good thing too.

There's also a prefix and suffix comparison on strings, which will reduce the amount of code written for brute force string problems. Also, for containers like std::map and std::set, you will be able to check if an element exists using something like if (a.contains(element)), which would be better than the much more dangerous if (a.count(element)) which blows up to $$$O(frequency)$$$ for multisets.

For some (warning: very rare) constant-factor optimization, [[likely]] and [[unlikely]] attributes would be a compiler-agnostic feature (no more using GCC's __builtin_expect anymore, so yay). Also as someone told me yesterday, C++20's [[no_unique_address]] can be useful for optimizing away empty structs.