How high above the Earth's surface are insects able to fly?

Three factors affect an insect's ability to fly high, the oxygen levels, the thinness of the air, and the temperature. The alpine bumblebees live at 3.25km above sea level. They were found to be able to fly in lab thin air equivalent to around 9 km but the air temperature would be way too cold for their muscles.

https://www.sciencefocus.com/nature/how-high-can-insects-fly

I have seen written that some butterflies have been found as high as 6,000 meters in elevation, however, a specific breed is not listed. The highest flying butterfly I found is Piercolias forsteri a butterfly that flies up to 4,200 meters in the Andes mountains.

https://www.nhm.ac.uk/discover/record-breaking-butterflies.html