guess I got what I deserved for this sin -_-
https://codereview.stackexchange.com/questions/252686/whats-wrong-with-my-midpoint
The video just describes a particular implementation, standard is still the same standard, that you can get for free in the draft form, or have to buy in a final form for some reason. This function if from C++20 standard, but you don't really need the document, it's a very simple function to describe, it just takes any two arithmetic types and returns their midpoint/average, more precisely what mathematical formulas a+(b-a)/2 or (a+b)/2 would give you. It's not easy to implement though, that's why they added it to the standard.
I see, they got offended that I considered libstdc++ standard library mailing list before them
https://codereview.stackexchange.com/posts/252686/revisions
probably the main reason they closed it