This is only true for poor quality coffee. The hot temperature masks defects (bitterness). Good coffee tastes better as it cools. https://www.baristamagazine.com/the-temperature-paradox-why-...
"This doesn’t mean drinking room-temperature coffee exclusively. The complete experience encompasses the entire temperature journey." and "High temperatures deliver immediate aromatic impact—the unique, irreplaceable value of fresh coffee."
I'm also not sure bitterness should be considered a defect in coffee, it's part of the flavor profile and actually peaks in perception at a higher temperature according to that article.
There is so many different ways and subjective taste palettes that I don't think there is one way. When I was younger and in a rush, I always drank my espresso maybe 30-60 seconds after they made it, the heat became part of what I enjoyed (eventually). Now I let it cool down to just above room-temperature if I know the place has good beans/roast as I feel even more flavor then. If I'm drinking a Americano, then it pretty much ends up room temperature before I even start drinking it.
Then we have my neighbor who I end up at the same cafe in sometimes, who poor their espresso into a glass of ice, then drink it, and they seem to enjoy their coffee just as much as me, so in the end, I don't think there is a right way here :)