How high can manned subsonic planes go? What is the maximum altitude a manned plane that flies subsonically can reach? Subsonic airplanes can't go as high as super- and hypersonic ones of course, so record holders are the latter ones. But ironically, the altitude record for leveled flight is set by the subsonic NASA Helios propeller aircraft at ~97,000 ft. However that's an uncrewed and weird-looking one. Can manned airplanes that fly subsonically go above the Armstrong line (60-63,000 ft) and higher (either in leveled or in parabolic flight), considering realistic fuel limitations? How high can subsonic airplanes go compared to supersonic ones?
76,000 feet.  Airbus Perlan Mission II glider, Sept 2, 2018.
The U-2 has a higher service ceiling, 80,000 feet, but it hasn't reached that.
(Perlan II's service ceiling is 90,000 feet.)