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Several military airplanes, including fighters, can and do fly that high and more. I never said anything about navigation risks - that was from other posters. Obviously space debris is a much higher daily risk, for satellites.

Um, the Air Force still uses the U-2. As does NASA.

https://en.wikipedia.org/wiki/Lockheed_U-2#Operators

The F-15 and Eurofighter Typhoon have published service ceilings of 65000ft, put them in a vertical climb and they will go a lot higher than that, the Streak Eagle reached 103000ft.

Still can't see any risk. You won't find F-15s flying that high except if they need to shoot a balloon.