I bought an infrared thermometer to help with that. I'm very sensitive to hot foods so that window is pretty narrow for me. I only start to drink when it approaches 130F (a little over is fine).

Lance Hendrick is kind of the ice queen of coffee and promotes brewing and drinking at quite cool temps. He's said below 50C and even I think below 44C as recommended temps. I'd avoid over 60C at least. I think that's around the range where some data has even suggested higher rates of throat cancer with chronic exposure. Personally I now set my Ember at 123F (50C) which is about as low as I'm comfortable going presently. It is true that more complex flavor profiles tend to reveal themselves at cooler temperatures (closer to body temp - 37C)

I grew up on piping hot coffee so it took me a while to get used to drinking at more medium temperatures instead. The taste buds don't work fully unless you're closer to room temperature, so if you're drinking fancy coffee it's sort of a waste. Still drink around 60-61°C, which I suppose is a fair few degrees too hot really.

I sometimes put my coffee mug (one of the soup-bowl-size ones) on a candle warmer to keep it warm. Especially in winter when I’m playing games, because my place is cold af to save money and my attention is elsewhere just long enough for it to go from scalding to ice before I remember it.

But also because I just continually top off my existing cup with new coffee from an insulated carafe, and that means no new warm cup, just a slightly less cold cup.

Either that or your temp sensing cells have all up and died.

Brewing into a carafe and then pouring small amounts into a mug is the best solution for achieving drinkable temps in the shortest time possible.